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alistair23-linux/tools/perf/util/cpumap.c

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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>
2010-03-10 02:36:09 -07:00
#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();
}