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OpenVMS Distributed Lock Manager Performance

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OpenVMS Distributed Lock Manager Performance Powered By Docstoc
					OpenVMS Distributed Lock
Manager Performance
Session ES-09-U

Keith Parris
HPQ
Background
   VMS system managers have
    traditionally looked at performance in 3
    areas:
     CPU
     Memory
     I/O
   But in VMS clusters, what may appear to
    be an I/O bottleneck can actually be a
    lock-related issue
Overview
 VMS keeps some lock activity data that
  no existing performance management
  tools look at
 Locking statistics and lock-related
  symptoms can provide valuable clues in
  detecting disk, adapter, or interconnect
  saturation problems
Overview
   The VMS Lock Manager does an excellent job under a
    wide variety of conditions to optimize locking activity
    and minimize overhead, but:
       In clusters with identical nodes running the same
        applications, remastering can sometimes happen too often
       In extremely large clusters, nodes can “gang up” on lock
        master nodes and overload them
       Locking activity can contribute to:
         CPU 0 saturation in Interrupt State
         Spinlock contention (Multi-Processor Synchronization time)
    We‟ll look at methods of detection, and solutions to,
    these types of problems
Topics
 Available monitoring tools for the Lock
  Manager
 How to map VMS symbolic lock
  resource names to real physical entities
 Lock request latencies
 How to measure lock rates
Topics
   Lock mastership, and why one might care
    about it
   Dynamic lock remastering
   How to detect and prevent lock mastership
    thrashing
   How to find the lock master node for a given
    resource tree
   How to force lock mastership of a given
    resource tree to a specific node
Topics
 Lock queues, their causes, and how to
  detect them
 Examples of problem locking scenarios
 How to measure pent-up remastering
  demand
Monitoring tools
   MONITOR utility
       MONITOR   LOCK
       MONITOR   DLOCK
       MONITOR   RLOCK (in VMS 7.3 and above; not 7.2-2)
       MONITOR   CLUSTER
       MONITOR   SCS
   SHOW CLUSTER /CONTINUOUS
   DECamds / Availability Manager
   DECps (Computer Associates‟ Unicenter
    Performance Management for OpenVMS,
    earlier Advise/IT)
Monitoring tools
    ANALYZE/SYSTEM
     New SHOW LOCK qualifiers for VMS 7.2 and above:
        /WAITING
            Displays only the waiting lock requests (those blocked
             by other locks)
        /SUMMARY
            Displays summary data and performance counters
     New SHOW RESOURCE qualifier for VMS 7.2 and above:
        /CONTENTION
            Displays resources which are under contention
Monitoring tools
    ANALYZE/SYSTEM
     New SDA extension LCK for lock tracing in VMS 7.2-2 and
      above
        SDA> LCK    !Shows help text with command summary
     Can display various additional lock manager statistics:
        SDA> LCK STATISTIC       !Shows lock manager statistics
     Can show busiest resource trees by lock activity rate:
        SDA> LCK SHOW ACTIVE !Shows lock activity
     Can trace lock requests:
        SDA> LCK LOAD            !Load the debug execlet
        SDA> LCK START TRACE     !Start tracing lock requests
        SDA> LCK STOP TRACE      !Stop tracing
        SDA> LCK SHOW TRACE      !Display contents of trace buffer
     Can even trigger remaster operations:
        SDA> LCK REMASTER        !Trigger a remaster operation
Mapping symbolic lock
resource names to real entities
   Techniques for mapping resource
    names to lock types
       Common prefixes:
        SYS$ for VMS executive
        F11B$ for XQP, file system
        RMS$ for Record Management Services
       See Appendix H in Alpha V1.5 IDSM or
        Appendix A in Alpha V7.0 version
Resource names
   Example: XQP File Serialization Lock
       Resource name format is
         “F11B$s” {Lock Basis}
         Parent lock is the Volume Allocation Lock
          “F11B$v” {Lock Volume Name}
       Calculate File ID from Lock Basis
         Lock Basis is RVN and File Number from File ID
          (ignoring Sequence Number), packed into 1
          longword
       Identify disk volume from parent resource
        name
Resource names
    Identifying file from File ID
      Look at file headers in Index File to get filespec:
         Can use DUMP utility to display file header (from
          Index File)
             $ DUMP /HEADER /IDENTIFIER=(file_id)
              /BLOCK=COUNT=0 disk:[000000]INDEXF.SYS
         Follow directory backlinks to determine directory path
         See example procedure FILE_ID_TO_NAME.COM
      (or use LIB$FID_TO_NAME routine to do all
       this, if sequence number can be obtained)
Resource names
   Example: RMS lock tree for an RMS indexed
    file:
       Resource name format is
         “RMS$” {File ID} {Flags byte} {Lock Volume Name}
       Identify filespec using File ID
       Flags byte indicates shared or private disk mount
       Pick up disk volume name
         This is label as of time disk was mounted
   Sub-locks are used for buckets and records
    within the file
Internal Structure of an RMS
Indexed File
RMS Data Bucket Contents

                     Data Bucket
       Data Record             Data Record

       Data Record             Data Record

       Data Record             Data Record

       Data Record             Data Record

       Data Record             Data Record
RMS Indexed File
Bucket and Record Locks
   Sub-locks of RMS File Lock
       Have to look at Parent lock to identify file
   Bucket lock:
       4 bytes: VBN of first block of the bucket
   Record lock:
       8 bytes (6 on VAX): Record File Address
        (RFA) of record
Locks and File I/O
   Lock requests and data transfers for a
    typical RMS indexed file I/O
    (prior to 7.2-1H1):
    1) Lock & get root index bucket
    2) Lock & get index buckets for any additional index
      levels
    3) Lock & get data bucket containing record
    4) Lock record
    5) For writes: write data bucket containing record
    Note: Most data reads may be avoided thanks to
      RMS global buffer cache
Locks and File I/O
   Since all indexed I/Os access Root Index
    Bucket, contention on lock for Root
    Index Bucket of hot file can be a
    bottleneck
   Lookup by Record File Address (RFA)
    avoids index lookup on 2nd and
    subsequent accesses to a record
Lock Request Latencies
   Latency depends on several things:
       Directory lookup needed or not
        Local or remote directory node
     $ENQ or $DEQ operation
     Local or remote lock master
        If remote, type of interconnect
Directory Lookups
   This is how VMS finds out which node is the
    lock master
   Only needed for 1st lock request on a
    particular resource tree on a given node
       Resource Block (RSB) remembers master node
        CSID
   Basic conceptual algorithm: Hash resource
    name and index into lock directory vector,
    which has been created based on
    LOCKDIRWT values
Lock Request Latencies
 Local requests are fastest
 Remote requests are significantly
  slower:
     Code path ~20 times longer
     Interconnect also contributes latency
     Total latency up to 2 orders of magnitude
      higher than local requests
Lock Request Latency
Client process on same node:
4-6 microseconds


            Lock Master Node

         Client
Lock Request Latency
Client across CI star coupler:
440 microseconds

   Lock Master             Client node
                              Client


                  Star
                 Coupler




                 Storage
Lock Request Latencies
How to measure lock rates
   VMS keeps counters of lock activity for
    each resource tree
       but not for each of the sub-resources
   So you can see the lock rate for an RMS
    indexed file, for example
       but not for individual buckets or records
        within that file
   SDA extension LCK can trace all lock
    requests if needed
Identifying busiest lock trees
in the cluster with a program
   Measure lock rates based on RSB data:
     Follow chain of root RSBs from
      LCK$GQ_RRSFL listhead via
      RSB$Q_RRSFL links
     Root RSBs contain counters:
        RSB$W_OACT: Old activity field (average lock
         rate per 8 second interval)
          Divide by 8 to get per-second average
        RSB$W_NACT: New activity (locks so far within
         current 8-second interval)
          Transient value, so not as useful
Identifying busiest lock trees
in the cluster with a program
   Look for non-zero OACT values:
       Gather resource name, master node CSID,
        and old-activity field
 Do this on each node
 Summarize data across the cluster
   See example procedure LOCK_ACTV.COM
    and program LCKACT.MAR
       Or, for VMS 7.2-2 and above:
         SDA> LCK SHOW ACTIVE
            Note: Per-node data, not cluster-wide summary
 Lock Activity Program Example
0000002020202020202020203153530200004C71004624534D52 RMS$F.qL...SS1   ...
    RMS lock tree for file [70,19569,0] on volume SS1
    File specification: DISK$SS1:[DATA8]PDATA.IDX;1
        Total: 11523
       *XYZB12   6455
        XYZB11    746
        XYZB14    611
        XYZB15    602
        XYZB23    564
        XYZB13    540
        XYZB19    532
        XYZB16    523
        XYZB20    415
        XYZB22    284
        XYZB18    127
        XYZB21    125

       * Lock Master Node for the resource

{This is a fairly hot file. Here the lock master node is optimal.}
  Lock Activity Program Example
0000002020202032454C494653595302000000D3000C24534D52 RMS$.......SYSFILE2   ...
    RMS lock tree for file [12,211,0] on volume SYSFILE2
    File specification: DISK$SYSFILE2:[SYSFILE2]SYSUAF.DAT;5
        Total:    184
        XYZB16     75
        XYZB20     48
        XYZB23     41
        XYZB21     16
        XYZB19      2
       *XYZB15      1
        XYZB13      1
        XYZB14      0
        XYZB12      0

{This reflects user logins, process creations, password changes, and such.
Note the poor lock master node selection here (XYZB16 would be optimal).}
Example: Application
(re)opens file frequently
 Symptom: High lock rate on File Access
  Arbitration Lock for application data file
 Cause: BASIC program re-executing
  OPEN command for a file; BASIC
  dutifully closes and then re-opens file
 Fix: Modify BASIC program to execute
  OPEN statement only once at image
  startup time
  Lock Activity Program Example
00000016202020202020202031505041612442313146 F11B$aAPP1        ....
    Files-11 File Access Arbitration lock for file [22,*,0] on volume APP1
    File specification: DISK$APP1:[DATA]XDATA.IDX;1
        Total:     50
       *XYZB15      8
        XYZB21      7
        XYZB16      7
        XYZB19      6
        XYZB20      6
        XYZB23      6
        XYZB18      5
        XYZB13      3
        XYZB12      1
        XYZB22      1
        XYZB14      1

{This shows where the application is apparently opening (or re-opening) this
particular file 50 times per second.}
Lock Mastership (Resource
Mastership) concept
 One lock master node is selected by
  VMS for a given resource tree at a given
  time
 Different resource trees may have
  different lock master nodes
Lock Mastership (Resource
Mastership) concept
 Lock master remembers all locks on a
  given resource tree for the entire cluster
 Each node holding locks also
  remembers the locks it is holding on
  resources, to allow recovery if lock
  master node dies
Lock Mastership
   Lock mastership node may change for
    various reasons:
     Lock master node goes down -- new master
      must be elected
     VMS may move lock mastership to a
      “better” node for performance reasons
        LOCKDIRWT imbalance found, or
        Activity-based Dynamic Lock Remastering
        Lock Master node no longer has interest
Lock Remastering
   Circumstances under which remastering
    occurs, and does not:
       LOCKDIRWT values
         VMS tends to remaster to node with higher
          LOCKDIRWT values, never to node with lower
          LOCKDIRWT
       Shifting initiated based on activity counters
        in root RSB
         PE1 parameter being non-zero can prevent
          movement or place threshold on lock tree size
       Shift if existing lock master loses interest
Lock Remastering
   VMS rules for dynamic remastering
    decision based on activity levels:
        assuming equal LOCKDIRWT values
     1) Must meet general threshold of 80 lock
      requests so far (LCK$GL_SYS_THRSH)
     2) New potential master node must have at
      least 10 more requests per second than
      current master (LCK$GL_ACT_THRSH)
Lock Remastering
   VMS rules for dynamic remastering:
       3) Estimated cost to move (based on size of
        lock tree) must be less than estimated
        savings (based on lock rate)
        except if new master meets criteria (2) for 3
         consecutive 8-second intervals, cost is ignored
       4) No more than 5 remastering operations
        can be going on at once on a node
        (LCK$GL_RM_QUOTA)
Lock Remastering
   VMS rules for dynamic remastering:
     5) If PE1 on the current master has a
      negative value, remastering trees off the
      node is disabled
     6) If PE1 has a positive, non-zero value on
      the current master, the tree must be smaller
      than PE1 in size or it will not be remastered
Lock Remastering
   Implications of dynamic remastering
    rules:
     LOCKDIRWT must be equal for lock activity
      levels to control choice of lock master node
     PE1 can be used to control movement of
      lock trees OFF of a node, but not ONTO a
      node
     RSB stores lock activity counts, so even
      high activity counts can be lost if the last
      lock is DEQueued on a given node and thus
      the RSB gets deallocated
Lock Remastering
   Implications of dynamic remastering
    rules:
       With two or more large CPUs of equal size
        running the same application, lock
        mastership “thrashing” is not uncommon:
        10 more lock requests per second is not much
         of a difference when you may be doing 100s or
         1,000s of lock requests per second
        Whichever new node becomes lock master may
         then see its own lock rate slow somewhat due to
         the remote lock request workload
Lock Remastering
    Lock mastership thrashing results in user-visible
     delays
      Lock operations on a tree are stalled during a remaster
       operation
      Locks and Resources were sent over 1 per SCS message
      Remastering large lock trees could take a long time
         e.g. 10 to 50 seconds for 15K lock tree size, prior to 7.2-2
      Improvement in VMS in version 7.2-2 and above gives
       very significant performance gain
         by using 64 Kbyte block data transfers instead of sending 1
          SCS message per RSB or LKB
How to Detect Lock Mastership
Thrashing
   Detection of remastering activity
       MONITOR RLOCK in 7.3 and above (not 7.2-2)
       SDA> SHOW LOCK/SUMMARY in 7.2 and above
       Change of mastership node for a given resource
       Check message counters under SDA:
         SDA> EXAMINE PMS$GL_RM_RBLD_SENT
         SDA> EXAMINE PMS$GL_RM_RBLD_RCVD
            Counts which increase suddenly by a large amount indicate
             remastering of large tree(s)
                SENT: Off of this node
                RCVD: Onto this node
            See example procedures WATCH_RBLD.COM and
             RBLD.COM
How to Prevent Lock
Mastership Thrashing
 Unbalanced node power
 Unequal workloads
 Unequal values of LOCKDIRWT
 Non-zero values of PE1
How to find the lock master
node for a given resource tree
   1) Take out a Null lock on the root
    resource using $ENQ
       VMS does directory lookup and finds out
        master node
   2) Use $GETLKI to identify the current
    lock master node‟s CSID and the lock
    count
       If the local node is the lock master, and the
        lock count is 1 (i.e. only our NL lock),
        there‟s no interest in the resource now
How to find the lock master
node for a given resource tree
 3) $DEQ to release the lock
 4) Use $GETSYI to translate the CSID to
  an SCS Nodename
 See example procedure
  FINDMASTER_FILE.COM and program
  FINDMASTER.MAR, which can find the
  lock master node for RMS file resource
  trees
Controlling Lock Mastership
   Lock Remastering is a good thing
       Maximizes the number of lock requests which are
        local (and thus fastest) by trying to move lock
        mastership of a tree to the node with the most
        activity on that tree
   So why would you want to wrest control of
    lock mastership away from VMS?
       Spread lock mastership workload more evenly
        across nodes to help avoid saturation of any single
        lock master node
       Provide best performance for a specific job by
        guaranteeing local locking for its files
How to force lock mastership of a
resource tree to a specific node
   3 ways to induce VMS to move a lock
    tree:
    1) Generate a lot of I/Os
      For example, run several copies of a program
       that rapidly accesses the file
    2) Generate a lot of lock requests
      without the associated I/O operations
    3) Generate the effect of a lot of lock requests
      without actually doing them
      by modifying VMS‟ data structures
How to force lock mastership of a
resource tree to a specific node
   We‟ll examine:
       1) Method using documented features
        thus fully supported
       2) Method modifying VMS data structures
Controlling Lock Mastership
Using Supported Methods
   To move a lock tree to a particular node
    (non-invasive method):
        Assume PE1 non-zero on all nodes to start with
     1) Set PE1 to 0 on existing lock master
      node to allow dynamic lock remastering of
      tree off that node
     2) Set PE1 to negative value (or small
      positive value) on target node to prevent
      lock tree from moving off of it afterward
Controlling Lock Mastership
Using Supported Methods
  3) On target node, take out a Null lock on
   root resource
  4) Take out a sub-lock of the parent Null
   lock, and then repeatedly convert it
   between Null and some other mode
       Check periodically to see if tree has moved
       yet (using $GETLKI)
  5) Once tree has moved, free locks
  6) Set PE1 back to original value on former
   master node
Controlling Lock Mastership
Using Supported Methods
    Pros:
      Uses only supported interfaces to VMS
    Cons:
      Generates significant load on existing lock master, from
       which you may have been trying to off-load work. In some
       cases, node may thus be saturated and unable to initiate
       lock remastering
      Programs running locally on existing lock master can
       generate so many requests that tree won‟t move because
       you can‟t generate nearly as many lock requests remotely
    See example program LOTSALOX.MAR
Controlling Lock Mastership By
Modifying VMS Data Structures
 Goal: Reproduce effect of lots of lock
  requests without the overhead of the
  lock requests actually occurring
 General Method: Modify activity-related
  counts and remastering-related fields
  and flags in root RSB to persuade VMS
  to remaster the resource tree
Controlling Lock Mastership By
Modifying VMS Data Structures
 1) Run program on node which is
  presently lock master
 2) Use $GETSYI to get CSID of desired
  target node, given nodename
 3) Lock down code and data
 4) $CMKRNL, raise IPL, grab LCKMGR
  spinlock
Controlling Lock Mastership By
Modifying VMS Data Structures
 5) Starting at LCK$GQ_RRSFL listhead,
  follow chain of root RSBs via
  RSB$Q_RRSFL links
 6) Search for root RSB with matching
  resource name, access mode, and
  group (0=System)
Controlling Lock Mastership By
Modifying VMS Data Structures
   7) Set up to trigger remaster operation:
     Set RSB$L_RM_CSID to target node„s CSID
     Set RSB$B_LSTCSID_IDX to low byte of
      target node‟s CSID
     Set RSB$B_SAME_CNT to 3 or more so
      remastering occurs regardless of cost
Controlling Lock Mastership By
Modifying VMS Data Structures
     Zero our activity counts RSB$W_OACT and
      RSB$W_NACT so local lock rate seems low
     Set new-master activity count
      RSB$W_NMACT to maximum possible (hex
      FFFF) to simulate tons of locking activity
     Set RSB$M_RM_PEND flag in
      RSB$L_STATUS field to indicate a remaster
      operation is now pending
   8) Release LCKMGR spinlock, lower IPL,
    and let VMS do its job
Controlling Lock Mastership By
Modifying VMS Data Structures
   Problem (for all methods):
       Once PE1 is set to zero to allow the desired lock
        tree to migrate, other lock trees may also migrate,
        unwanted
   Solution:
       To prevent this, in all other resource trees
        mastered on this node:
         Clear RM_PEND flag in L_STATUS if set, and
            Set W_OACT and W_NACT to max. (hex FFFF)
            Zero W_NMACT, L_RM_CSID, B_LSTCSID_IDX, and
             B_SAME_CNT
Controlling Lock Mastership By
Modifying VMS Data Structures
       Pros:
        Does the job reliably
        Can avoid other resource trees “escaping”
       Cons:
        High-IPL code presents some level of risk of
         crashing a system
       See example program REMASTER.MAR
   One might instead use (in 7.2-2 & above)
       SDA> LCK REMASTER
Causes of lock queues
 Program bug (e.g. not freeing a record
  lock)
 I/O or interconnect saturation
 “Deadman” locks
How to detect lock queues
 Using DECamds / Availability Manager
 Using SDA
 Using other methods
Lock contention & DECamds
 DECamds can identify lock contention if
  a lock blocks others for 15 seconds
 AMDS$LOCK_LOG.LOG file in
  AMDS$SYSTEM: contains a log of
  occurrences of suspected contention
 Resource name decoding techniques
  shown earlier can sometimes be used to
  identify the file involved
 Deadman locks can be filtered out
Detecting Lock Queues with
ANALYZE/SYSTEM (SDA)
   New qualifier added to SHOW RESOURCE
    command in SDA for 7.2 and above:
       SHOW RESOURCE/CONTENTION shows blocking
        and blocked lock requests
   New qualifier was added to SHOW LOCK
    command in SDA for 7.2 and above:
       SHOW LOCK/WAITING displays blocked lock
        requests (but then you must determine what‟s
        blocking them)
Detecting Lock Queues with a
program
 Traverse lock database starting with
  LCK$GQ_RRSFL listhead and following
  chain of root RSBs via RSB$Q_RRSFL
  links
 Within each resource tree, follow
  RSB$Q_SRSFL chain to examine all
  sub-resources, recursively
Detecting Lock Queues with a
program
   Check the Wait Queue (RSB$Q_WTQFL and
    RSB$Q_WTQBL)
   Check the Convert Queue (RSB$Q_CVTQFL
    and RSB$Q_CVTQBL)
   If queues are found, display:
       Queue length(s)
       Resource name
       Resource names for all parent locks, up to the root lock
   See example DCL procedure LCKQUE.COM
    and program LCKQUE.MAR
Example: Directory File Grows
Large
 Symptom: High queue length on file
  serialization lock for .DIR file
 Cause: Directory file has grown to over
  127 blocks
       (VMS version 7.1-2 or earlier; 7.2 and later
        are much less sensitive to this problem)
   Fix: Delete or rename files out of
    directory
   Lock Queue Program Example
Here are examples where a directory file got very large under 7.1-2:

'F11B$vAPP2        ' 202020202020202032505041762442313146
    Files-11 Volume Allocation lock for volume APP2
 'F11B$sH...' 00000148732442313146
    Files-11 File Serialization lock for file [328,*,0] on volume APP2
    File specification: DISK$APP2:[]DATA.DIR;1
  Convert queue: 0, Wait queue: 95


'F11B$vLOGFILE     ' 2020202020454C4946474F4C762442313146
    Files-11 Volume Allocation lock for volume LOGFILE
'F11B$s....' 00000A2E732442313146
    Files-11 File Serialization lock for file [2606,*,0] on volume LOGFILE
    File specification: DISK$LOGFILE:[000000]LOGS.DIR;1
  Convert queue: 0, Wait queue: 3891
Example: Fragmented File
Header
   Symptom: High queue length on File
    Serialization Lock for application data file
   Cause: CONVERTs onto disk without
    sufficient contiguous space resulted in
    highly-fragmented files, increasing I/O load on
    disk array. File was so fragmented it had 3
    extension file headers
   Fix: Defragment disk, or do an /IMAGE
    Backup/Restore
 Lock Queue Program Example
Here's an example of the result of reorganizing RMS indexed files with
$CONVERTs over a weekend without enough contiguous free space available,
causing a lot of file fragmentation, and dramatically increasing the
I/O load on a RAID array on the next busy day (we had to fix this with
a backup/restore cycle soon after). The file shown here had gotten so
fragmented as to have 3 extension file headers. The lock we're queueing
on here is the file serialization lock for this RMS indexed file:

'F11B$s....' 0000000E732442313146
  Files-11 File Serialization lock for file [14,*,0] on volume THDATA
  File specification: DISK$THDATA:[TH]OT.IDX;1
Convert queue: 0, Wait queue: 28
Future Directions for this
Investigation Work
   Concern: Locking down remastering
    with PE1 (to avoid lock mastership
    thrashing) can result in sub-optimal lock
    master node selections over time
Future Directions for this
Investigation Work
   Possible ways of mitigating side-effects of
    preventing remastering using PE1:
       Adjust PE1 value as high as you can without
        producing noticeable delays
       Upgrade to 7.2-2 or above for more-efficient
        remastering
       Set PE1 to 0 for short periods, periodically
       Raise fixed threshold values in VMS data cells
        LCK$GL_SYS_THRSH and particularly
        LCK$GL_ACT_THRSH
       More-invasive automatic monitoring and control of
        remastering activity
       Enhancements to VMS itself
How to measure pent-up
remastering demand
   While PE1 is set to prevent remastering,
    sub-optimal lock mastership may result
       VMS will “want” to move some lock trees
        but cannot
   See example procedure LCKRM.COM
    and program LCKRM.MAR, which
    measure pent-up remastering demand
How to measure pent-up
remastering demand
LCKRM example:
Time: 16:19

----- XYZB12: -----

'RMS$..I....SS1 ...' 000000202020202020202020315353020000084900B424534D52
    RMS lock tree for file [180,2121,0] on volume SS1
    File specification: DISK$SS1:[PDATA]PDATA.IDX;1
      Pent-up demand for remaster operation is pending
        to node XYZB18 (CSID 00010031)
          Last CSID Index: 34, Same-count: 0
        Average lock rates: Local 44, Remote 512
        Status bits:
            RM_PEND
Interrupt-state/stack saturation
 Too much lock mastership workload can
  saturate primary CPU on a node
 See with MONITOR MODES/CPU=0/ALL
Interrupt-state/stack saturation
   FAST_PATH:
       Can shift interrupt-state workload off primary CPU in SMP
        systems
         IO_PREFER_CPUS value of an even number disables CPU 0 use
              Consider limiting interrupts to a subset of non-primaries
       FAST_PATH for CI since 7.0
       FAST_PATH for MC “never”
       FAST_PATH for SCSI and FC is in 7.3 and above
       FAST_PATH for LANs (e.g. FDDI & Ethernet) slated for 7.3-1
       Even with FAST_PATH enabled, CPU 0 still receives the
        device interrupt, but hands it off immediately via an inter-
        processor interrupt
         7.3-1 is slated to allow FAST_PATH interrupts to bypass CPU 0
          entirely and go directly to a non-primary CPU
Dedicated-CPU Lock Manager
   With 7.2-2 and above, you can choose to
    dedicate a CPU to do lock management work.
    This may help reduce MP_SYNC time.
   LCKMGR_MODE parameter:
        0 = Disabled
       >1 = Enable if at least this many CPUs are running
   LCKMGR_CPUID parameter specifies which
    CPU to dedicate to LCKMGR_SERVER
    process
Example programs
   Programs referenced herein may be found:
       On the VMS Freeware V5 CD, under directories
        [KP_LOCKTOOLS] or [KP_CLUSTERTOOLS]
       or on the web at:
         http://www.openvms.compaq.com/freeware/freeware50/kp_clustertools/
         http://www.openvms.compaq.com/freeware/freeware50/kp_locktools/

       New additions & corrections may be found at:
         http://encompasserve.org/~parris/
Example programs
   Copies of this presentation (and others)
    may be found at:
       http://www.geocities.com/keithparris/
Questions?
    Speaker Contact Info:

    Keith Parris
E-mail: parris@encompasserve.org
or keithparris@yahoo.com
or Keith.Parris@hp.com
Web: http://encompasserve.org/~parris/
and http://www.geocities.com/keithparris/

				
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