[tip:perfcounters/core] perf report: Add per system call overhead histogram

tip-bot for Ingo Molnar
2009-06-15T14:09:16Z

Commit-ID: 3dfabc74c65904c9e6cf952391312d16ea772ef5
Gitweb: http://git.kernel.org/tip/3dfabc74c65904c9e6cf952391312d16ea772ef5
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Mon, 15 Jun 2009 11:24:38 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 15 Jun 2009 15:58:03 +0200

perf report: Add per system call overhead histogram

Take advantage of call-graph percounter sampling/recording to
display a non-trivial histogram: the true, collapsed/summarized
cost measurement, on a per system call total overhead basis:

aldebaran:~/linux/linux/tools/perf> ./perf record -g -a -f ~/hackbench 10
aldebaran:~/linux/linux/tools/perf> ./perf report -s symbol --syscalls | head -10
#
# (3536 samples)
#
# Overhead Symbol
# ........ ......
#
40.75% [k] sys_write
40.21% [k] sys_read
4.44% [k] do_nmi
...

This is done by accounting each (reliable) call-chain that chains back
to a given system call to that system call function.

[ So in the above example we can see that hackbench spends about 40% of
its total time somewhere in sys_write() and 40% somewhere in
sys_read(), the rest of the time is spent in user-space. The time
is not spent in sys_write() _itself_ but in one of its many child
functions. ]

Or, a recording of a (source files are already in the page-cache) kernel build:

$ perf record -g -m 512 -f -- make -j32 kernel
$ perf report -s s --syscalls | grep '\[k\]' | grep -v nmi

4.14% [k] do_page_fault
1.20% [k] sys_write
1.10% [k] sys_open
0.63% [k] sys_exit_group
0.48% [k] smp_apic_timer_interrupt
0.37% [k] sys_read
0.37% [k] sys_execve
0.20% [k] sys_mmap
0.18% [k] sys_close
0.14% [k] sys_munmap
0.13% [k] sys_poll
0.09% [k] sys_newstat
0.07% [k] sys_clone
0.06% [k] sys_newfstat
0.05% [k] sys_access
0.05% [k] schedule

Shows the true total cost of each syscall variant that gets used
during a kernel build. This profile reveals it that pagefaults are
the costliest, followed by read()/write().

An interesting detail: timer interrupts cost 0.5% - or 0.5 seconds
per 100 seconds of kernel build-time. (this was done with HZ=1000)

The summary is done in 'perf report', i.e. in the post-processing
stage - so once we have a good call-graph recording, this type of
non-trivial high-level analysis becomes possible.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
tools/perf/builtin-report.c | 12 ++++++++++++
1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index aebba56..1e2f5dd 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -40,6 +40,7 @@ static int dump_trace = 0;

static int verbose;
static int full_paths;
+static int collapse_syscalls;

static unsigned long page_size;
static unsigned long mmap_window = 32;
@@ -983,6 +984,15 @@ process_overflow_event(event_t *event, unsigned long offset, unsigned long head)
for (i = 0; i < chain->nr; i++)
dprintf("..... %2d: %p\n", i, (void *)chain->ips[i]);
}
+ if (collapse_syscalls) {
+ /*
+ * Find the all-but-last kernel entry
+ * amongst the call-chains - to get
+ * to the level of system calls:
+ */
+ if (chain->kernel >= 2)
+ ip = chain->ips[chain->kernel-2];
+ }
}

dprintf(" ... thread: %s:%d\n", thread->comm, thread->pid);
@@ -1343,6 +1353,8 @@ static const struct option options[] = {
"sort by key(s): pid, comm, dso, symbol. Default: pid,symbol"),
OPT_BOOLEAN('P', "full-paths", &full_paths,
"Don't shorten the pathnames taking into account the cwd"),
+ OPT_BOOLEAN('S', "syscalls", &collapse_syscalls,
+ "show per syscall summary overhead, using call graph"),
OPT_END()
};