lockstat.1

.TH LOCKSTAT 1M "Jan 27, 2014"
.SH NAME
lockstat \- report kernel lock and profiling statistics
.SH SYNOPSIS
.LP
.nf
\fBlockstat\fR [\fB-ACEHI\fR] [\fB-e\fR \fIevent_list\fR] [\fB-i\fR \fIrate\fR]
     [\fB-b\fR | \fB-t\fR | \fB-h\fR | \fB-s\fR \fIdepth\fR] [\fB-n\fR \fInrecords\fR]
     [\fB-l\fR \fIlock\fR [, \fIsize\fR]] [\fB-d\fR \fIduration\fR]
     [\fB-f\fR \fIfunction\fR [, \fIsize\fR]] [\fB-T\fR] [\fB-ckgwWRpP\fR] [\fB-D\fR \fIcount\fR]
     [\fB-o\fR \fIfilename\fR] [\fB-x\fR \fIopt\fR [=val]] \fIcommand\fR [\fIargs\fR]
.fi

.SH DESCRIPTION
.sp
.LP
The \fBlockstat\fR utility gathers and displays kernel locking and profiling
statistics. \fBlockstat\fR 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, \fBlockstat\fR 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.
.sp
.LP
\fBlockstat\fR gathers data until the specified command completes. For example,
to gather statistics for a fixed-time interval, use \fBsleep\fR(1) as the
command, as follows:
.sp
.LP
\fBexample#\fR \fBlockstat\fR \fBsleep\fR \fB5\fR
.sp
.LP
When the \fB-I\fR option is specified, \fBlockstat\fR establishes a
per-processor high-level periodic interrupt source to gather profiling data.
The interrupt handler simply generates a \fBlockstat\fR event whose caller is
the interrupted PC (program counter). The profiling event is just like any
other \fBlockstat\fR event, so all of the normal \fBlockstat\fR options are
applicable.
.sp
.LP
\fBlockstat\fR 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 \fBlockstat\fR is restricted to super-user by
default. The system administrator can permit other users to use \fBlockstat\fR
by granting them additional DTrace privileges. Refer to the \fISolaris Dynamic
Tracing Guide\fR for more information about DTrace security features.
.SH OPTIONS
.sp
.LP
The following options are supported:
.SS "Event Selection"
.sp
.LP
If no event selection options are specified, the default is \fB-C\fR.
.sp
.ne 2
.na
\fB\fB-A\fR\fR
.ad
.sp .6
.RS 4n
Watch all lock events. \fB-A\fR is equivalent to \fB-CH\fR.
.RE

.sp
.ne 2
.na
\fB\fB-C\fR\fR
.ad
.sp .6
.RS 4n
Watch contention events.
.RE

.sp
.ne 2
.na
\fB\fB-E\fR\fR
.ad
.sp .6
.RS 4n
Watch error events.
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-e\fR \fIevent_list\fR\fR
.ad
.sp .6
.RS 4n
Only watch the specified events. \fIevent\fR \fIlist\fR is a comma-separated
list of events or ranges of events such as 1,4-7,35. Run \fBlockstat\fR with no
arguments to get a brief description of all events.
.RE

.sp
.ne 2
.na
\fB\fB-H\fR\fR
.ad
.sp .6
.RS 4n
Watch hold events.
.RE

.sp
.ne 2
.na
\fB\fB-I\fR\fR
.ad
.sp .6
.RS 4n
Watch profiling interrupt events.
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-i\fR \fIrate\fR\fR
.ad
.sp .6
.RS 4n
Interrupt rate (per second) for \fB-I\fR. The default is 97 Hz, so that
profiling doesn't run in lockstep with the clock interrupt (which runs at 100
Hz).
.RE

.SS "Data Gathering"
.sp
.ne 2
.na
\fB\fB-x\fR \fIarg\fR[=\fIval\fR]\fR
.ad
.sp .6
.RS 4n
Enable or modify a DTrace runtime option or D compiler option. The list of
options is found in the \fI\fR. Boolean options are enabled by specifying their
name. Options with values are set by separating the option name and value with
an equals sign (=).
.RE

.SS "Data Gathering (Mutually Exclusive)"
.sp
.ne 2
.na
\fB\fB-b\fR\fR
.ad
.sp .6
.RS 4n
Basic statistics: lock, caller, number of events.
.RE

.sp
.ne 2
.na
\fB\fB-h\fR\fR
.ad
.sp .6
.RS 4n
Histogram: Timing plus time-distribution histograms.
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-s\fR \fIdepth\fR\fR
.ad
.sp .6
.RS 4n
Stack trace: Histogram plus stack traces up to \fIdepth\fR frames deep.
.RE

.sp
.ne 2
.na
\fB\fB-t\fR\fR
.ad
.sp .6
.RS 4n
Timing: Basic plus timing for all events [default].
.RE

.SS "Data Filtering"
.sp
.ne 2
.na
\fB\fB\fR\fB-d\fR \fIduration\fR\fR
.ad
.sp .6
.RS 4n
Only watch events longer than \fIduration\fR.
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-f\fR \fIfunc[,size]\fR\fR
.ad
.sp .6
.RS 4n
Only watch events generated by \fIfunc\fR, which can be specified as a symbolic
name or hex address. \fIsize\fR defaults to the \fBELF\fR symbol size if
available, or \fB1\fR if not.
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-l\fR \fIlock[,size]\fR\fR
.ad
.sp .6
.RS 4n
Only watch \fIlock\fR, which can be specified as a symbolic name or hex
address. \fBsize\fR defaults to the \fBELF\fR symbol size or \fB1\fR if the
symbol size is not available.
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-n\fR \fInrecords\fR\fR
.ad
.sp .6
.RS 4n
Maximum number of data records.
.RE

.sp
.ne 2
.na
\fB\fB-T\fR\fR
.ad
.sp .6
.RS 4n
Trace (rather than sample) events [off by default].
.RE

.SS "Data Reporting"
.sp
.ne 2
.na
\fB\fB-c\fR\fR
.ad
.sp .6
.RS 4n
Coalesce lock data for lock arrays (for example, \fBpse_mutex[]\fR).
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-D\fR \fIcount\fR\fR
.ad
.sp .6
.RS 4n
Only display the top \fIcount\fR events of each type.
.RE

.sp
.ne 2
.na
\fB\fB-g\fR\fR
.ad
.sp .6
.RS 4n
Show total events generated by function. For example, if \fBfoo()\fR calls
\fBbar()\fR in a loop, the work done by \fBbar()\fR counts as work generated by
\fBfoo()\fR (along with any work done by \fBfoo()\fR itself). The \fB-g\fR
option works by counting the total number of stack frames in which each
function appears. This implies two things: (1) the data reported by \fB-g\fR
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 \fB-g\fR is \fB-s\fR
\fB50\fR.
.RE

.sp
.ne 2
.na
\fB\fB-k\fR\fR
.ad
.sp .6
.RS 4n
Coalesce PCs within functions.
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-o\fR \fIfilename\fR\fR
.ad
.sp .6
.RS 4n
Direct output to \fIfilename\fR.
.RE

.sp
.ne 2
.na
\fB\fB-P\fR\fR
.ad
.sp .6
.RS 4n
Sort data by (\fIcount * time\fR) product.
.RE

.sp
.ne 2
.na
\fB\fB-p\fR\fR
.ad
.sp .6
.RS 4n
Parsable output format.
.RE

.sp
.ne 2
.na
\fB\fB-R\fR\fR
.ad
.sp .6
.RS 4n
Display rates (events per second) rather than counts.
.RE

.sp
.ne 2
.na
\fB\fB-W\fR\fR
.ad
.sp .6
.RS 4n
Whichever: distinguish events only by caller, not by lock.
.RE

.sp
.ne 2
.na
\fB\fB-w\fR\fR
.ad
.sp .6
.RS 4n
Wherever: distinguish events only by lock, not by caller.
.RE

.SH DISPLAY FORMATS
.sp
.LP
The following headers appear over various columns of data.
.sp
.ne 2
.na
\fB\fBCount\fR or \fBops/s\fR\fR
.ad
.sp .6
.RS 4n
Number of times this event occurred, or the rate (times per second) if \fB-R\fR
was specified.
.RE

.sp
.ne 2
.na
\fB\fBindv\fR\fR
.ad
.sp .6
.RS 4n
Percentage of all events represented by this individual event.
.RE

.sp
.ne 2
.na
\fB\fBgenr\fR\fR
.ad
.sp .6
.RS 4n
Percentage of all events generated by this function.
.RE

.sp
.ne 2
.na
\fB\fBcuml\fR\fR
.ad
.sp .6
.RS 4n
Cumulative percentage; a running total of the individuals.
.RE

.sp
.ne 2
.na
\fB\fBrcnt\fR\fR
.ad
.sp .6
.RS 4n
Average reference count. This will always be \fB1\fR for exclusive locks
(mutexes, spin locks, rwlocks held as writer) but can be greater than \fB1\fR
for shared locks (rwlocks held as reader).
.RE

.sp
.ne 2
.na
\fB\fBnsec\fR\fR
.ad
.sp .6
.RS 4n
Average duration of the events in nanoseconds, as appropriate for the event.
For the profiling event, duration means interrupt latency.
.RE

.sp
.ne 2
.na
\fB\fBLock\fR\fR
.ad
.sp .6
.RS 4n
Address of the lock; displayed symbolically if possible.
.RE

.sp
.ne 2
.na
\fB\fBCPU\fR\fR
.ad
.sp .6
.RS 4n
\fBCPU\fR, reported as \fBcpu[id].\fR
.RE

.sp
.ne 2
.na
\fB\fBCaller\fR\fR
.ad
.sp .6
.RS 4n
Address of the caller; displayed symbolically if possible.
.RE

.SH EXAMPLES
.LP
\fBExample 1 \fRMeasuring Kernel Lock Contention
.sp
.in +2
.nf
example# \fBlockstat sleep 5\fR
Adaptive mutex spin: 2210 events in 5.055 seconds (437 events/sec)
.fi
.in -2
.sp

.sp
.in +2
.nf
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
[...]
.fi
.in -2
.sp

.LP
\fBExample 2 \fRMeasuring Hold Times
.sp
.in +2
.nf
example# \fBlockstat -H -D 10 sleep 1\fR
Adaptive mutex spin: 513 events
.fi
.in -2
.sp

.sp
.in +2
.nf
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
-------------------------------------------------------------------------
[...]
.fi
.in -2
.sp

.LP
\fBExample 3 \fRMeasuring Hold Times for Stack Traces Containing a Specific
Function
.sp
.in +2
.nf
example# \fBlockstat -H -f tcp_rput_data -s 50 -D 10 sleep 1\fR
Adaptive mutex spin: 11 events in 1.023 seconds (11
events/sec)
.fi
.in -2
.sp

.sp
.in +2
.nf
-------------------------------------------------------------------------
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
-------------------------------------------------------------------------
[...]
.fi
.in -2
.sp

.LP
\fBExample 4 \fRBasic Kernel Profiling
.sp
.LP
For basic profiling, we don't care whether the profiling interrupt sampled
\fBfoo()\fR\fB+0x4c\fR or \fBfoo()\fR\fB+0x78\fR; we care only that it sampled
somewhere in \fBfoo()\fR, so we use \fB-k\fR. The \fBCPU\fR and \fBPIL\fR
aren't relevant to basic profiling because we are measuring the system as a
whole, not a particular \fBCPU\fR or interrupt level, so we use \fB-W\fR.

.sp
.in +2
.nf
example# \fBlockstat -kIW -D 20 ./polltest\fR
Profiling interrupt: 82 events in 0.424 seconds (194
events/sec)
.fi
.in -2
.sp

.sp
.in +2
.nf
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
-----------------------------------------------------------------------
[...]
.fi
.in -2
.sp

.LP
\fBExample 5 \fRGenerated-load Profiling
.sp
.LP
In the example above, 5% of the samples were in \fBpoll()\fR. This tells us how
much time was spent inside \fBpoll()\fR itself, but tells us nothing about how
much work was \fBgenerated\fR by \fBpoll()\fR; that is, how much time we spent
in functions called by \fBpoll()\fR. To determine that, we use the \fB-g\fR
option. The example below shows that although \fBpolltest\fR spends only 5% of
its time in \fBpoll()\fR itself, \fBpoll()\fR-induced work accounts for 34% of
the load.

.sp
.LP
Note that the functions that generate the profiling interrupt
(\fBlockstat_intr()\fR, \fBcyclic_fire()\fR, 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
\fBnot\fR add up to 100% because they are not independent. If 72% of all stack
traces contain both \fBfoo()\fR and \fBbar()\fR, then both \fBfoo()\fR and
\fBbar()\fR are 72% load generators.

.sp
.in +2
.nf
example# \fBlockstat -kgIW -D 20 ./polltest\fR
Profiling interrupt: 80 events in 0.412 seconds (194 events/sec)
.fi
.in -2
.sp

.sp
.in +2
.nf
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
-------------------------------------------------------------------------
[...]
.fi
.in -2
.sp

.LP
\fBExample 6 \fRGathering Lock Contention and Profiling Data for a Specific
Module
.sp
.LP
In this example we use the \fB-f\fR option not to specify a single function,
but rather to specify the entire text space of the \fBsbus\fR module. We gather
both lock contention and profiling statistics so that contention can be
correlated with overall load on the module.

.sp
.in +2
.nf
example# \fBmodinfo | grep sbus\fR
 24 102a8b6f   b8b4  59   1  sbus (SBus (sysio) nexus driver)
.fi
.in -2
.sp

.sp
.in +2
.nf
example# \fBlockstat -kICE -f 0x102a8b6f,0xb8b4 sleep 10\fR
Adaptive mutex spin: 39 events in 10.042 seconds (4 events/sec)
.fi
.in -2
.sp

.sp
.in +2
.nf
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
-------------------------------------------------------------------------
[...]
.fi
.in -2
.sp

.LP
\fBExample 8 \fRDetermining which Subsystem is Causing the System to be Busy
.sp
.in +2
.nf
example# \fBlockstat -s 10 -I sleep 20\fR

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 \e
                                               _mutex_hold+0x70
                                               ghd_waitq_process_and \e
                                               _mutex_exit+0x4
                                               ghd_transport+0x12c
                                               ata_disk_tran_start+0x108
-----------------------------------------------------------------------
[...]
.fi
.in -2
.sp

.SH SEE ALSO
.sp
.LP
\fBdtrace\fR(1M), \fBplockstat\fR(1M)
.sp
.LP
\fISolaris Dynamic Tracing Guide\fR
.SH NOTES
.sp
.LP
The profiling support provided by \fBlockstat\fR \fB-I\fR replaces the old (and
undocumented) \fB/usr/bin/kgmon\fR and \fB/dev/profile\fR.
.sp
.LP
Tail-call elimination can affect call sites. For example, if
\fBfoo()\fR\fB+0x50\fR calls \fBbar()\fR and the last thing \fBbar()\fR does is
call \fBmutex_exit()\fR, the compiler can arrange for \fBbar()\fR to branch to
\fBmutex_exit()\fRwith a return address of \fBfoo()\fR\fB+0x58\fR. Thus, the
\fBmutex_exit()\fR in \fBbar()\fR will appear as though it occurred at
\fBfoo()\fR\fB+0x58\fR.
.sp
.LP
The \fBPC\fR 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.
.sp
.LP
When using the \fB-I\fR and \fB-s\fR 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 \fBPC\fR.
.sp
.LP
The \fBlockstat\fR technology is provided on an as-is basis. The format and
content of \fBlockstat\fR output reflect the current Darwin kernel
implementation and are therefore subject to change in future releases.