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perf tools: Fix sparse CPU numbering related bugs

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At present, the perf subcommands that do system-wide monitoring
(perf stat, perf record and perf top) don't work properly unless
the online cpus are numbered 0, 1, ..., N-1.  These tools ask
for the number of online cpus with sysconf(_SC_NPROCESSORS_ONLN)
and then try to create events for cpus 0, 1, ..., N-1.

This creates problems for systems where the online cpus are
numbered sparsely.  For example, a POWER6 system in
single-threaded mode (i.e. only running 1 hardware thread per
core) will have only even-numbered cpus online.

This fixes the problem by reading the /sys/devices/system/cpu/online
file to find out which cpus are online.  The code that does that is in
tools/perf/util/cpumap.[ch], and consists of a read_cpu_map()
function that sets up a cpumap[] array and returns the number of
online cpus.  If /sys/devices/system/cpu/online can't be read or
can't be parsed successfully, it falls back to using sysconf to
ask how many cpus are online and sets up an identity map in cpumap[].

The perf record, perf stat and perf top code then calls
read_cpu_map() in the system-wide monitoring case (instead of
sysconf) and uses cpumap[] to get the cpu numbers to pass to
perf_event_open.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: Anton Blanchard <anton@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
LKML-Reference: <20100310093609.GA3959@brick.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul Mackerras
2010-03-10 20:36:09 +11:00
committed by Ingo Molnar
parent 220b140b52
commit a12b51c478
6 changed files with 81 additions and 13 deletions
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10
tools/perf/builtin-stat.c
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@ -45,6 +45,7 @@
#include "util/event.h"
#include "util/debug.h"
#include "util/header.h"
#include "util/cpumap.h"
#include <sys/prctl.h>
#include <math.h>
@ -151,7 +152,7 @@ static void create_perf_stat_counter(int counter, int pid)
unsigned int cpu;
for (cpu = 0; cpu < nr_cpus; cpu++) {
fd[cpu][counter] = sys_perf_event_open(attr, -1, cpu, -1, 0);
fd[cpu][counter] = sys_perf_event_open(attr, -1, cpumap[cpu], -1, 0);
if (fd[cpu][counter] < 0 && verbose)
fprintf(stderr, ERR_PERF_OPEN, counter,
fd[cpu][counter], strerror(errno));
@ -519,9 +520,10 @@ int cmd_stat(int argc, const char **argv, const char *prefix __used)
nr_counters = ARRAY_SIZE(default_attrs);
}
nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
assert(nr_cpus <= MAX_NR_CPUS);
assert((int)nr_cpus >= 0);
if (system_wide)
nr_cpus = read_cpu_map();
else
nr_cpus = 1;
/*
* We dont want to block the signals - that would cause