LOCKSTAT(1M)

NAME
lockstat - report kernel lock and profiling statistics

SYNOPSIS

lockstat [-ACEHI] [-e event_list] [-i rate]
     [-b | -t | -h | -s depth] [-n nrecords]
     [-l lock [, size]] [-d duration]
     [-f function [, size]] [-T] [-ckgwWRpP] [-D count]
     [-o filename] [-x opt [=val]] command [args]

DESCRIPTION

The lockstat utility gathers and displays kernel locking and profiling statistics. lockstat allows you to specify which events to watch (for example, spin on adaptive mutex, block on read access to rwlock due to waiting writers, and so forth) how much data to gather for each event, and how to display the data. By default, lockstat monitors all lock contention events, gathers frequency and timing data about those events, and displays the data in decreasing frequency order, so that the most common events appear first.

lockstat gathers data until the specified command completes. For example, to gather statistics for a fixed-time interval, use sleep(1) as the command, as follows:

example# lockstat sleep 5

When the -I option is specified, lockstat establishes a per-processor high-level periodic interrupt source to gather profiling data. The interrupt handler simply generates a lockstat event whose caller is the interrupted PC (program counter). The profiling event is just like any other lockstat event, so all of the normal lockstat options are applicable.

lockstat relies on DTrace to modify the running kernel's text to intercept events of interest. This imposes a small but measurable overhead on all system activity, so access to lockstat is restricted to super-user by default. The system administrator can permit other users to use lockstat by granting them additional DTrace privileges. Refer to the Solaris Dynamic Tracing Guide for more information about DTrace security features.

OPTIONS

The following options are supported:

  Event Selection

If no event selection options are specified, the default is -C.

-A

    Watch all lock events. -A is equivalent to -CH.

-C

    Watch contention events.

-E

    Watch error events.

-e event_list

    Only watch the specified events. event list is a comma-separated list of events or ranges of events such as 1,4-7,35. Run lockstat with no arguments to get a brief description of all events.

-H

    Watch hold events.

-I

    Watch profiling interrupt events.

-i rate

    Interrupt rate (per second) for -I. The default is 97 Hz, so that profiling doesn't run in lockstep with the clock interrupt (which runs at 100 Hz).

  Data Gathering

-x arg[=val]

    Enable or modify a DTrace runtime option or D compiler option. The list of options is found in the . Boolean options are enabled by specifying their name. Options with values are set by separating the option name and value with an equals sign (=).

  Data Gathering (Mutually Exclusive)

-b

    Basic statistics: lock, caller, number of events.

-h

    Histogram: Timing plus time-distribution histograms.

-s depth

    Stack trace: Histogram plus stack traces up to depth frames deep.

-t

    Timing: Basic plus timing for all events [default].

  Data Filtering

-d duration

    Only watch events longer than duration.

-f func[,size]

    Only watch events generated by func, which can be specified as a symbolic name or hex address. size defaults to the ELF symbol size if available, or 1 if not.

-l lock[,size]

    Only watch lock, which can be specified as a symbolic name or hex address. size defaults to the ELF symbol size or 1 if the symbol size is not available.

-n nrecords

    Maximum number of data records.

-T

    Trace (rather than sample) events [off by default].

  Data Reporting

-c

    Coalesce lock data for lock arrays (for example, pse_mutex[]).

-D count

    Only display the top count events of each type.

-g

    Show total events generated by function. For example, if foo() calls bar() in a loop, the work done by bar() counts as work generated by foo() (along with any work done by foo() itself). The -g option works by counting the total number of stack frames in which each function appears. This implies two things: (1) the data reported by -g can be misleading if the stack traces are not deep enough, and (2) functions that are called recursively might show greater than 100% activity. In light of issue (1), the default data gathering mode when using -g is -s 50.

-k

    Coalesce PCs within functions.

-o filename

    Direct output to filename.

-P

    Sort data by (count * time) product.

-p

    Parsable output format.

-R

    Display rates (events per second) rather than counts.

-W

    Whichever: distinguish events only by caller, not by lock.

-w

    Wherever: distinguish events only by lock, not by caller.

DISPLAY FORMATS

The following headers appear over various columns of data.

Count or ops/s

    Number of times this event occurred, or the rate (times per second) if -R was specified.

indv

    Percentage of all events represented by this individual event.

genr

    Percentage of all events generated by this function.

cuml

    Cumulative percentage; a running total of the individuals.

rcnt

    Average reference count. This will always be 1 for exclusive locks (mutexes, spin locks, rwlocks held as writer) but can be greater than 1 for shared locks (rwlocks held as reader).

nsec

    Average duration of the events in nanoseconds, as appropriate for the event. For the profiling event, duration means interrupt latency.

Lock

    Address of the lock; displayed symbolically if possible.

CPU

    CPU, reported as cpu[id].

Caller

    Address of the caller; displayed symbolically if possible.

EXAMPLES

Example 1 Measuring Kernel Lock Contention

example# lockstat sleep 5
Adaptive mutex spin: 2210 events in 5.055 seconds (437 events/sec)

Count indv cuml rcnt     nsec Lock                Caller
------------------------------------------------------------------------
  269  12%  12% 1.00     2160 service_queue       background+0xdc
  249  11%  23% 1.00       86 service_queue       qenable_locked+0x64
  228  10%  34% 1.00      131 service_queue       background+0x15c
   68   3%  37% 1.00       79 0x30000024070       untimeout+0x1c
   59   3%  40% 1.00      384 0x300066fa8e0       background+0xb0
   43   2%  41% 1.00       30 rqcred_lock         svc_getreq+0x3c
   42   2%  43% 1.00      341 0x30006834eb8       background+0xb0
   41   2%  45% 1.00      135 0x30000021058       untimeout+0x1c
   40   2%  47% 1.00       39 rqcred_lock         svc_getreq+0x260
   37   2%  49% 1.00     2372 0x300068e83d0       hmestart+0x1c4
   36   2%  50% 1.00       77 0x30000021058       timeout_common+0x4
   36   2%  52% 1.00      354 0x300066fa120       background+0xb0
   32   1%  53% 1.00       97 0x30000024070       timeout_common+0x4
   31   1%  55% 1.00     2923 0x300069883d0       hmestart+0x1c4
   29   1%  56% 1.00      366 0x300066fb290       background+0xb0
   28   1%  57% 1.00      117 0x3000001e040       untimeout+0x1c
   25   1%  59% 1.00       93 0x3000001e040       timeout_common+0x4
   22   1%  60% 1.00       25 0x30005161110       sync_stream_buf+0xdc
   21   1%  60% 1.00      291 0x30006834eb8       putq+0xa4
   19   1%  61% 1.00       43 0x3000515dcb0       mdf_alloc+0xc
   18   1%  62% 1.00      456 0x30006834eb8       qenable+0x8
   18   1%  63% 1.00       61 service_queue       queuerun+0x168
   17   1%  64% 1.00      268 0x30005418ee8       vmem_free+0x3c
[...]
R/W reader blocked by writer: 76 events in 5.055 seconds (15 events/sec)
Count indv cuml rcnt     nsec Lock                Caller
------------------------------------------------------------------------
   23  30%  30% 1.00 22590137 0x300098ba358       ufs_dirlook+0xd0
   17  22%  53% 1.00  5820995 0x3000ad815e8       find_bp+0x10
   13  17%  70% 1.00  2639918 0x300098ba360       ufs_iget+0x198
    4   5%  75% 1.00  3193015 0x300098ba360       ufs_getattr+0x54
    3   4%  79% 1.00  7953418 0x3000ad817c0       find_bp+0x10
    3   4%  83% 1.00   935211 0x3000ad815e8       find_read_lof+0x14
    2   3%  86% 1.00 16357310 0x300073a4720       find_bp+0x10
    2   3%  88% 1.00  2072433 0x300073a4720       find_read_lof+0x14
    2   3%  91% 1.00  1606153 0x300073a4370       find_bp+0x10
    1   1%  92% 1.00  2656909 0x300107e7400       ufs_iget+0x198
[...]

Example 2 Measuring Hold Times

example# lockstat -H -D 10 sleep 1
Adaptive mutex spin: 513 events

Count indv cuml rcnt     nsec Lock                Caller
-------------------------------------------------------------------------
  480   5%   5% 1.00     1136 0x300007718e8       putnext+0x40
  286   3%   9% 1.00      666 0x3000077b430       getf+0xd8
  271   3%  12% 1.00      537 0x3000077b430       msgio32+0x2fc
  270   3%  15% 1.00     3670 0x300007718e8       strgetmsg+0x3d4
  270   3%  18% 1.00     1016 0x300007c38b0       getq_noenab+0x200
  264   3%  20% 1.00     1649 0x300007718e8       strgetmsg+0xa70
  216   2%  23% 1.00     6251 tcp_mi_lock         tcp_snmp_get+0xfc
  206   2%  25% 1.00      602 thread_free_lock    clock+0x250
  138   2%  27% 1.00      485 0x300007c3998       putnext+0xb8
  138   2%  28% 1.00     3706 0x300007718e8       strrput+0x5b8
-------------------------------------------------------------------------
[...]

Example 3 Measuring Hold Times for Stack Traces Containing a Specific Function

example# lockstat -H -f tcp_rput_data -s 50 -D 10 sleep 1
Adaptive mutex spin: 11 events in 1.023 seconds (11
events/sec)

-------------------------------------------------------------------------
Count indv cuml rcnt     nsec Lock                   Caller
    9  82%  82% 1.00     2540 0x30000031380          tcp_rput_data+0x2b90
      nsec ------ Time Distribution ------ count     Stack
       256 |@@@@@@@@@@@@@@@@               5         tcp_rput_data+0x2b90
       512 |@@@@@@                         2         putnext+0x78
      1024 |@@@                            1         ip_rput+0xec4
      2048 |                               0         _c_putnext+0x148
      4096 |                               0         hmeread+0x31c
      8192 |                               0         hmeintr+0x36c
     16384 |@@@                            1
sbus_intr_wrapper+0x30
[...]
Count indv cuml rcnt     nsec Lock                   Caller
    1   9%  91% 1.00     1036 0x30000055380          freemsg+0x44
      nsec ------ Time Distribution ------ count     Stack
      1024 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1         freemsg+0x44
                                                     tcp_rput_data+0x2fd0
                                                     putnext+0x78
                                                     ip_rput+0xec4
                                                     _c_putnext+0x148
                                                     hmeread+0x31c
                                                     hmeintr+0x36c
sbus_intr_wrapper+0x30
-------------------------------------------------------------------------
[...]

Example 4 Basic Kernel Profiling

For basic profiling, we don't care whether the profiling interrupt sampled foo()+0x4c or foo()+0x78; we care only that it sampled somewhere in foo(), so we use -k. The CPU and PIL aren't relevant to basic profiling because we are measuring the system as a whole, not a particular CPU or interrupt level, so we use -W.

example# lockstat -kIW -D 20 ./polltest
Profiling interrupt: 82 events in 0.424 seconds (194
events/sec)

Count indv cuml rcnt     nsec Hottest CPU         Caller
-----------------------------------------------------------------------
    8  10%  10% 1.00      698 cpu[1]              utl0
    6   7%  17% 1.00      299 master_cpu          read
    5   6%  23% 1.00      124 cpu[1]              getf
    4   5%  28% 1.00      327 master_cpu          fifo_read
    4   5%  33% 1.00      112 cpu[1]              poll
    4   5%  38% 1.00      212 cpu[1]              uiomove
    4   5%  43% 1.00      361 cpu[1]              mutex_tryenter
    3   4%  46% 1.00      682 master_cpu          write
    3   4%  50% 1.00       89 master_cpu          pcache_poll
    3   4%  54% 1.00      118 cpu[1]              set_active_fd
    3   4%  57% 1.00      105 master_cpu          syscall_trap32
    3   4%  61% 1.00      640 cpu[1]              (usermode)
    2   2%  63% 1.00      127 cpu[1]              fifo_poll
    2   2%  66% 1.00      300 cpu[1]              fifo_write
    2   2%  68% 1.00      669 master_cpu          releasef
    2   2%  71% 1.00      112 cpu[1]              bt_getlowbit
    2   2%  73% 1.00      247 cpu[1]              splx
    2   2%  76% 1.00      503 master_cpu          mutex_enter
    2   2%  78% 1.00      467 master_cpu          disp_lock_enter
    2   2%  80% 1.00      139 cpu[1]              default_copyin
-----------------------------------------------------------------------
[...]

Example 5 Generated-load Profiling

In the example above, 5% of the samples were in poll(). This tells us how much time was spent inside poll() itself, but tells us nothing about how much work was generated by poll(); that is, how much time we spent in functions called by poll(). To determine that, we use the -g option. The example below shows that although polltest spends only 5% of its time in poll() itself, poll()-induced work accounts for 34% of the load.

Note that the functions that generate the profiling interrupt (lockstat_intr(), cyclic_fire(), and so forth) appear in every stack trace, and therefore are considered to have generated 100% of the load. This illustrates an important point: the generated load percentages do not add up to 100% because they are not independent. If 72% of all stack traces contain both foo() and bar(), then both foo() and bar() are 72% load generators.

example# lockstat -kgIW -D 20 ./polltest
Profiling interrupt: 80 events in 0.412 seconds (194 events/sec)

Count genr cuml rcnt     nsec Hottest CPU         Caller
-------------------------------------------------------------------------
   80 100% ---- 1.00      310 cpu[1]              lockstat_intr
   80 100% ---- 1.00      310 cpu[1]              cyclic_fire
   80 100% ---- 1.00      310 cpu[1]              cbe_level14
   80 100% ---- 1.00      310 cpu[1]              current_thread
   27  34% ---- 1.00      176 cpu[1]              poll
   20  25% ---- 1.00      221 master_cpu          write
   19  24% ---- 1.00      249 cpu[1]              read
   17  21% ---- 1.00      232 master_cpu          write32
   17  21% ---- 1.00      207 cpu[1]              pcache_poll
   14  18% ---- 1.00      319 master_cpu          fifo_write
   13  16% ---- 1.00      214 cpu[1]              read32
   10  12% ---- 1.00      208 cpu[1]              fifo_read
   10  12% ---- 1.00      787 cpu[1]              utl0
    9  11% ---- 1.00      178 master_cpu          pcacheset_resolve
    9  11% ---- 1.00      262 master_cpu          uiomove
    7   9% ---- 1.00      506 cpu[1]              (usermode)
    5   6% ---- 1.00      195 cpu[1]              fifo_poll
    5   6% ---- 1.00      136 cpu[1]              syscall_trap32
    4   5% ---- 1.00      139 master_cpu          releasef
    3   4% ---- 1.00      277 cpu[1]              polllock
-------------------------------------------------------------------------
[...]

Example 6 Gathering Lock Contention and Profiling Data for a Specific Module

In this example we use the -f option not to specify a single function, but rather to specify the entire text space of the sbus module. We gather both lock contention and profiling statistics so that contention can be correlated with overall load on the module.

example# modinfo | grep sbus
 24 102a8b6f   b8b4  59   1  sbus (SBus (sysio) nexus driver)

example# lockstat -kICE -f 0x102a8b6f,0xb8b4 sleep 10
Adaptive mutex spin: 39 events in 10.042 seconds (4 events/sec)

Count indv cuml rcnt     nsec Lock               Caller
-------------------------------------------------------------------------
   15  38%  38% 1.00      206 0x30005160528      sync_stream_buf
    7  18%  56% 1.00       14 0x30005160d18      sync_stream_buf
    6  15%  72% 1.00       27 0x300060c3118      sync_stream_buf
    5  13%  85% 1.00       24 0x300060c3510      sync_stream_buf
    2   5%  90% 1.00       29 0x300060c2d20      sync_stream_buf
    2   5%  95% 1.00       24 0x30005161cf8      sync_stream_buf
    1   3%  97% 1.00       21 0x30005161110      sync_stream_buf
    1   3% 100% 1.00       23 0x30005160130      sync_stream_buf
[...]
Adaptive mutex block: 9 events in 10.042 seconds (1 events/sec)
Count indv cuml rcnt     nsec Lock               Caller
-------------------------------------------------------------------------
    4  44%  44% 1.00   156539 0x30005160528      sync_stream_buf
    2  22%  67% 1.00   763516 0x30005160d18      sync_stream_buf
    1  11%  78% 1.00   462130 0x300060c3510      sync_stream_buf
    1  11%  89% 1.00   288749 0x30005161110      sync_stream_buf
    1  11% 100% 1.00  1015374 0x30005160130      sync_stream_buf
[...]
Profiling interrupt: 229 events in 10.042 seconds (23 events/sec)
Count indv cuml rcnt     nsec Hottest CPU        Caller
-------------------------------------------------------------------------
   89  39%  39% 1.00      426 master_cpu         sync_stream_buf
   64  28%  67% 1.00      398 master_cpu         sbus_intr_wrapper
   23  10%  77% 1.00      324 master_cpu         iommu_dvma_kaddr_load
   21   9%  86% 1.00      512 master_cpu         iommu_tlb_flush
   14   6%  92% 1.00      342 master_cpu         iommu_dvma_unload
   13   6%  98% 1.00      306 cpu[1]             iommu_dvma_sync
    5   2% 100% 1.00      389 cpu[1]             iommu_dma_bindhdl
-------------------------------------------------------------------------
[...]

Example 8 Determining which Subsystem is Causing the System to be Busy

example# lockstat -s 10 -I sleep 20
Profiling interrupt: 4863 events in 47.375 seconds (103 events/sec)
Count indv cuml rcnt     nsec CPU              Caller
-----------------------------------------------------------------------
1929   40%  40% 0.00     3215 master_cpu       usec_delay+0x78
  nsec ------ Time Distribution ------ count   Stack
  4096 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  1872    ata_wait+0x90
  8192 |                               27      acersb_get_intr_status+0x34
 16384 |                               29      ata_set_feature+0x124
 32768 |                               1       ata_disk_start+0x15c
                                               ata_hba_start+0xbc
                                               ghd_waitq_process_and \
                                               _mutex_hold+0x70
                                               ghd_waitq_process_and \
                                               _mutex_exit+0x4
                                               ghd_transport+0x12c
                                               ata_disk_tran_start+0x108
-----------------------------------------------------------------------
[...]

SEE ALSO

dtrace(1M), plockstat(1M)

Solaris Dynamic Tracing Guide

NOTES

The profiling support provided by lockstat -I replaces the old (and undocumented) /usr/bin/kgmon and /dev/profile.

Tail-call elimination can affect call sites. For example, if foo()+0x50 calls bar() and the last thing bar() does is call mutex_exit(), the compiler can arrange for bar() to branch to mutex_exit()with a return address of foo()+0x58. Thus, the mutex_exit() in bar() will appear as though it occurred at foo()+0x58.

The PC in the stack frame in which an interrupt occurs can be bogus because, between function calls, the compiler is free to use the return address register for local storage.

When using the -I and -s options together, the interrupted PC will usually not appear anywhere in the stack since the interrupt handler is entered asynchronously, not by a function call from that PC.

The lockstat technology is provided on an as-is basis. The format and content of lockstat output reflect the current Darwin kernel implementation and are therefore subject to change in future releases.