On Mon, Jan 15, 2018 at 12:20:38PM -0800, [email protected] wrote:
> From: Kan Liang <[email protected]>
>
> The perf record has specific codes to calculate the ringbuffer position
> for both overwrite and non-overwrite mode. Now, only perf record
> supports both modes. The perf top will support both modes later.
> It is useful to make the specific codes generic.
>
> Introduce a new interface perf_mmap__read_init() to find ringbuffer
> position. The perf_mmap__read_init() is actually factored out from
> perf_mmap__push().
> There are slight differences.
> - Add a check for map->refcnt
> - Add new return value logic, EAGAIN and EINVAL.
not helpful.. I asked to separate those changes,
so we can clearly see what the refcnt check for
and what's behing that EAGAIN return
please add separate:
1) patch that adds perf_mmap__read_init into perf_mmap__push
with no functional change
2) patch adds adds and explain the refcnt check
3) patch that adds and explain the EAGAIN return
thanks,
jirka
>
> Signed-off-by: Kan Liang <[email protected]>
> ---
> tools/perf/util/mmap.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> tools/perf/util/mmap.h | 2 ++
> 2 files changed, 45 insertions(+)
>
> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
> index 05076e6..414089f 100644
> --- a/tools/perf/util/mmap.c
> +++ b/tools/perf/util/mmap.c
> @@ -267,6 +267,49 @@ static int overwrite_rb_find_range(void *buf, int mask,
> u64 head, u64 *start, u6
> return -1;
> }
>
> +/*
> + * Report the start and end of the available data in ringbuffer
> + */
> +int perf_mmap__read_init(struct perf_mmap *map, bool overwrite,
> + u64 *startp, u64 *endp)
> +{
> + unsigned char *data = map->base + page_size;
> + u64 head = perf_mmap__read_head(map);
> + u64 old = map->prev;
> + unsigned long size;
> +
> + /*
> + * Check if event was unmapped due to a POLLHUP/POLLERR.
> + */
> + if (!refcount_read(&map->refcnt))
> + return -EINVAL;
> +
> + *startp = overwrite ? head : old;
> + *endp = overwrite ? old : head;
> +
> + if (*startp == *endp)
> + return -EAGAIN;
> +
> + size = *endp - *startp;
> + if (size > (unsigned long)(map->mask) + 1) {
> + if (!overwrite) {
> + WARN_ONCE(1, "failed to keep up with mmap data. (warn
> only once)\n");
> +
> + map->prev = head;
> + perf_mmap__consume(map, overwrite);
> + return -EAGAIN;
> + }
> +
> + /*
> + * Backward ring buffer is full. We still have a chance to read
> + * most of data from it.
> + */
> + if (overwrite_rb_find_range(data, map->mask, head, startp,
> endp))
> + return -EINVAL;
> + }
> + return 0;
> +}
> +
> int perf_mmap__push(struct perf_mmap *md, bool overwrite,
> void *to, int push(void *to, void *buf, size_t size))
> {
> diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h
> index e43d7b5..0633308 100644
> --- a/tools/perf/util/mmap.h
> +++ b/tools/perf/util/mmap.h
> @@ -94,4 +94,6 @@ int perf_mmap__push(struct perf_mmap *md, bool backward,
>
> size_t perf_mmap__mmap_len(struct perf_mmap *map);
>
> +int perf_mmap__read_init(struct perf_mmap *map, bool overwrite,
> + u64 *startp, u64 *endp);
> #endif /*__PERF_MMAP_H */
> --
> 2.5.5
>
