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
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:
# 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.
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
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+Pri_Class
CPU plus the priority class of the interrupted thread. For
example, 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)
HISTORY
The lockstat utility first appeared in FreeBSD 7.1.
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
compiler can arrange for bar() to branch to mtx_unlock() with a return
address 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
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.
FreeBSD 13.1-RELEASE-p6 February 25, 2020 FreeBSD 13.1-RELEASE-p6
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