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SubjectRE: [PATCH V4 02/15] perf mmap: introduce perf_mmap__read_init()
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> On Mon, Jan 15, 2018 at 12:20:38PM -0800, kan.liang@intel.com wrote:
> > From: Kan Liang <kan.liang@intel.com>
> >
> > 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
>

Oh I see. I have misunderstood before.
I will change it in V5.

Thanks,
Kan


> thanks,
> jirka
>
> >
> > Signed-off-by: Kan Liang <kan.liang@intel.com>
> > ---
> > 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
> >

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