diff options
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/perf_counter.h | 22 |
1 files changed, 10 insertions, 12 deletions
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h index 90cce0c74a03..f2b914de3f0c 100644 --- a/include/linux/perf_counter.h +++ b/include/linux/perf_counter.h @@ -167,30 +167,28 @@ struct perf_counter_mmap_page { /* * Bits needed to read the hw counters in user-space. * - * The index and offset should be read atomically using the seqlock: - * - * __u32 seq, index; - * __s64 offset; + * u32 seq; + * s64 count; * * again: - * rmb(); * seq = pc->lock; - * * if (unlikely(seq & 1)) { * cpu_relax(); * goto again; * } * - * index = pc->index; - * offset = pc->offset; + * if (pc->index) { + * count = pmc_read(pc->index - 1); + * count += pc->offset; + * } else + * goto regular_read; * - * rmb(); + * barrier(); * if (pc->lock != seq) * goto again; * - * After this, index contains architecture specific counter index + 1, - * so that 0 means unavailable, offset contains the value to be added - * to the result of the raw timer read to obtain this counter's value. + * NOTE: for obvious reason this only works on self-monitoring + * processes. */ __u32 lock; /* seqlock for synchronization */ __u32 index; /* hardware counter identifier */ |