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LOCKSTAT(1)		FreeBSD	General	Commands Manual		   LOCKSTAT(1)

NAME
     lockstat -- report	kernel lock and	profiling statistics

SYNOPSIS
     lockstat [-ACEHIV]	[-e event-list]	[-i rate] [-b |	-t | -h	| -s depth]
	      [-n num-records] [-l lock	[,size]] [-d duration]
	      [-f function [,size]] [-T] [-kgwWRpP] [-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 con-
     tention 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 exam-
     ple, to gather statistics for a fixed-time	interval, use sleep(1) as the
     command, as follows:

	   # lockstat sleep 5

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

     lockstat relies on	DTrace to modify the running kernel's text to inter-
     cept 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.

OPTIONS
     The following options are supported:

     -V	     Print the D program used to gather	the requested data.

   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(1) runtime option or D compiler option.
	     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	num-records
	     Maximum number of data records.

     -T	     Trace (rather than	sample)	events.	 This is off by	default.

   Data	Reporting
     -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 gen-
	     erated 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 de-
	     fault 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 sec-
	     ond) 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 la-
	     tency.

     Lock    Address of	the lock; displayed symbolically if possible.

     CPU+Pri_Class
	     CPU plus the priority class of the	interrupted thread.  For exam-
	     ple, if CPU 4 is interrupted while	running	a timeshare thread,
	     this will be reported as `cpu[4]+TShar'.

     Caller  Address of	the caller; displayed symbolically if possible.

EXAMPLES
     Example 1 Measuring Kernel	Lock Contention

       # lockstat sleep	5

       Adaptive	mutex spin: 41411 events in 5.011 seconds (8263	events/sec)

       Count indv cuml rcnt	nsec Lock		    Caller
       -------------------------------------------------------------------------------
       13750  33%  33% 0.00	  72 vm_page_queue_free_mtx vm_page_free_toq+0x12e
       13648  33%  66% 0.00	  66 vm_page_queue_free_mtx vm_page_alloc+0x138
	4023  10%  76% 0.00	  51 vm_dom+0x80	    vm_page_dequeue+0x68
	2672   6%  82% 0.00	 186 vm_dom+0x80	    vm_page_enqueue+0x63
	 618   1%  84% 0.00	  31 0xfffff8000cd83a88	    qsyncvp+0x37
	 506   1%  85% 0.00	 164 0xfffff8000cb3f098	    vputx+0x5a
	 477   1%  86% 0.00	  69 0xfffff8000c7eb180	    uma_dbg_getslab+0x5b
	 288   1%  87% 0.00	  77 0xfffff8000cd8b000	    vn_finished_write+0x29
	 263   1%  88% 0.00	 103 0xfffff8000cbad448	    vinactive+0xdc
	 259   1%  88% 0.00	  53 0xfffff8000cd8b000	    vfs_ref+0x24
	 237   1%  89% 0.00	  20 0xfffff8000cbad448	    vfs_hash_get+0xcc
	 233   1%  89% 0.00	  22 0xfffff8000bfd9480	    uma_dbg_getslab+0x5b
	 223   1%  90% 0.00	  20 0xfffff8000cb3f098	    cache_lookup+0x561
	 193   0%  90% 0.00	  16 0xfffff8000cb40ba8	    vref+0x27
	 175   0%  91% 0.00	  34 0xfffff8000cbad448	    vputx+0x5a
	 169   0%  91% 0.00	  51 0xfffff8000cd8b000	    vfs_unbusy+0x27
	 164   0%  92% 0.00	  31 0xfffff8000cb40ba8	    vputx+0x5a
       [...]

       Adaptive	mutex block: 10	events in 5.011	seconds	(2 events/sec)

       Count indv cuml rcnt	nsec Lock		    Caller
       -------------------------------------------------------------------------------
	   3  30%  30% 0.00    17592 vm_page_queue_free_mtx vm_page_alloc+0x138
	   2  20%  50% 0.00    20528 vm_dom+0x80	    vm_page_enqueue+0x63
	   2  20%  70% 0.00    55502 0xfffff8000cb40ba8	    vputx+0x5a
	   1  10%  80% 0.00    12007 vm_page_queue_free_mtx vm_page_free_toq+0x12e
	   1  10%  90% 0.00	9125 0xfffff8000cbad448	    vfs_hash_get+0xcc
	   1  10% 100% 0.00	7864 0xfffff8000cd83a88	    qsyncvp+0x37
       -------------------------------------------------------------------------------
       [...]

     Example 2 Measuring Hold Times

       # lockstat -H -D	10 sleep 1

       Adaptive	mutex hold: 109589 events in 1.039 seconds (105526 events/sec)

       Count indv cuml rcnt	nsec Lock		    Caller
       -------------------------------------------------------------------------------
	8998   8%   8% 0.00	 617 0xfffff8000c7eb180	    uma_dbg_getslab+0xd4
	5901   5%  14% 0.00	 917 vm_page_queue_free_mtx vm_object_terminate+0x16a
	5040   5%  18% 0.00	 902 vm_dom+0x80	    vm_page_free_toq+0x88
	4884   4%  23% 0.00	1056 vm_page_queue_free_mtx vm_page_alloc+0x44e
	4664   4%  27% 0.00	 759 vm_dom+0x80	    vm_fault_hold+0x1a13
	4011   4%  31% 0.00	 888 vm_dom		    vm_page_advise+0x11b
	4010   4%  34% 0.00	 957 vm_dom+0x80	    _vm_page_deactivate+0x5c
	3743   3%  38% 0.00	 582 0xfffff8000cf04838	    pmap_is_prefaultable+0x158
	2254   2%  40% 0.00	 952 vm_dom		    vm_page_free_toq+0x88
	1639   1%  41% 0.00	 591 0xfffff800d60065b8	    trap_pfault+0x1f7
       -------------------------------------------------------------------------------
       [...]

       R/W writer hold:	64314 events in	1.039 seconds (61929 events/sec)

       Count indv cuml rcnt	nsec Lock		    Caller
       -------------------------------------------------------------------------------
	7421  12%  12% 0.00	2994 pvh_global_lock	    pmap_page_is_mapped+0xb6
	4668   7%  19% 0.00	3313 pvh_global_lock	    pmap_enter+0x9ae
	1639   3%  21% 0.00	 733 0xfffff80168d10200	    vm_object_deallocate+0x683
	1639   3%  24% 0.00	3061 0xfffff80168d10200	    unlock_and_deallocate+0x2b
	1639   3%  26% 0.00	2966 0xfffff80168d10200	    vm_fault_hold+0x16ee
	1567   2%  29% 0.00	 733 0xfffff80168d10200	    vm_fault_hold+0x19bc
	 821   1%  30% 0.00	 786 0xfffff801eb0cc000	    vm_object_madvise+0x32d
	 649   1%  31% 0.00	4918 0xfffff80191105300	    vm_fault_hold+0x16ee
	 648   1%  32% 0.00	8112 0xfffff80191105300	    unlock_and_deallocate+0x2b
	 647   1%  33% 0.00	1261 0xfffff80191105300	    vm_object_deallocate+0x683
       -------------------------------------------------------------------------------

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

       # lockstat -H -f	tcp_input -s 50	-D 10 sleep 1

       Adaptive	mutex hold: 68 events in 1.026 seconds (66 events/sec)

       -------------------------------------------------------------------------------
       Count indv cuml rcnt	nsec Lock		    Caller
	  32  47%  47% 0.00	1631 0xfffff800686f50d8	    tcp_do_segment+0x284b

	     nsec ------ Time Distribution ------ count	    Stack
	     1024 |@@@@@@@@@@			  11	    tcp_input+0xf54
	     2048 |@@@@@@@@@@@@@		  14	    ip_input+0xc8
	     4096 |@@@@@			  6	    swi_net+0x192
	     8192 |				  1	    intr_event_execute_handlers+0x93
							    ithread_loop+0xa6
							    fork_exit+0x84
							    0xffffffff808cf9ee
       -------------------------------------------------------------------------------
       Count indv cuml rcnt	nsec Lock		    Caller
	  29  43%  90% 0.00	4851 0xfffff800686f50d8	    sowakeup+0xf8

	     nsec ------ Time Distribution ------ count	    Stack
	     4096 |@@@@@@@@@@@@@@@		  15	    tcp_do_segment+0x2423
	     8192 |@@@@@@@@@@@@			  12	    tcp_input+0xf54
	    16384 |@@				  2	    ip_input+0xc8
							    swi_net+0x192
							    intr_event_execute_handlers+0x93
							    ithread_loop+0xa6
							    fork_exit+0x84
							    0xffffffff808cf9ee
       -------------------------------------------------------------------------------
       [...]

SEE ALSO
     dtrace(1),	ksyms(4), locking(9)

NOTES
     Tail-call elimination can affect call sites.  For example,	if foo()+0x50
     calls bar() and the last thing bar() does is call mtx_unlock(), the com-
     piler can arrange for bar() to branch to mtx_unlock() with	a return ad-
     dress of foo()+0x58. Thus,	the mtx_unlock() 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 be-
     cause, between function calls, the	compiler is free to use	the return ad-
     dress register for	local storage.

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

FreeBSD	13.0		      September	29, 2015		  FreeBSD 13.0

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | DISPLAY FORMATS | EXAMPLES | SEE ALSO | NOTES

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