diff options
Diffstat (limited to 'include/linux/perf_counter.h')
| -rw-r--r-- | include/linux/perf_counter.h | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h index 0d833228eee..8ac18852dcf 100644 --- a/include/linux/perf_counter.h +++ b/include/linux/perf_counter.h @@ -160,10 +160,45 @@ struct perf_counter_hw_event { struct perf_counter_mmap_page { __u32 version; /* version number of this structure */ __u32 compat_version; /* lowest version this is compat with */ + + /* + * 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; + * + * again: + * rmb(); + * seq = pc->lock; + * + * if (unlikely(seq & 1)) { + * cpu_relax(); + * goto again; + * } + * + * index = pc->index; + * offset = pc->offset; + * + * rmb(); + * 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. + */ __u32 lock; /* seqlock for synchronization */ __u32 index; /* hardware counter identifier */ __s64 offset; /* add to hardware counter value */ + /* + * Control data for the mmap() data buffer. + * + * User-space reading this value should issue an rmb(), on SMP capable + * platforms, after reading this value -- see perf_counter_wakeup(). + */ __u32 data_head; /* head in the data section */ }; |