linux/tools/perf/util/cpumap.c
Paul Mackerras a12b51c478 perf tools: Fix sparse CPU numbering related bugs
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>
2010-03-11 13:36:53 +01:00

59 lines
1,012 B
C

#include "util.h"
#include "../perf.h"
#include "cpumap.h"
#include <assert.h>
#include <stdio.h>
int cpumap[MAX_NR_CPUS];
static int default_cpu_map(void)
{
int nr_cpus, i;
nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
assert(nr_cpus <= MAX_NR_CPUS);
assert((int)nr_cpus >= 0);
for (i = 0; i < nr_cpus; ++i)
cpumap[i] = i;
return nr_cpus;
}
int read_cpu_map(void)
{
FILE *onlnf;
int nr_cpus = 0;
int n, cpu, prev;
char sep;
onlnf = fopen("/sys/devices/system/cpu/online", "r");
if (!onlnf)
return default_cpu_map();
sep = 0;
prev = -1;
for (;;) {
n = fscanf(onlnf, "%u%c", &cpu, &sep);
if (n <= 0)
break;
if (prev >= 0) {
assert(nr_cpus + cpu - prev - 1 < MAX_NR_CPUS);
while (++prev < cpu)
cpumap[nr_cpus++] = prev;
}
assert (nr_cpus < MAX_NR_CPUS);
cpumap[nr_cpus++] = cpu;
if (n == 2 && sep == '-')
prev = cpu;
else
prev = -1;
if (n == 1 || sep == '\n')
break;
}
fclose(onlnf);
if (nr_cpus > 0)
return nr_cpus;
return default_cpu_map();
}