Messages in this thread | | | Date | Thu, 11 Jan 2018 15:25:20 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH V3 02/12] perf mmap: factor out function to find ringbuffer position |
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On Thu, Dec 21, 2017 at 10:08:44AM -0800, kan.liang@intel.com wrote:
SNIP
> +/* > + * Report the start and end of the available data in ringbuffer > + */ > +int perf_mmap__read_init(struct perf_mmap *map, bool overwrite, > + u64 *start, u64 *end) > { > - u64 head = perf_mmap__read_head(md); > - u64 old = md->prev; > - u64 end = head, start = old; > - unsigned char *data = md->base + page_size; > + u64 head = perf_mmap__read_head(map); > + u64 old = map->prev; > + unsigned char *data = map->base + page_size; > unsigned long size; > - void *buf; > - int rc = 0; > > - start = overwrite ? head : old; > - end = overwrite ? old : head; > + /* > + * Check if event was unmapped due to a POLLHUP/POLLERR. > + */ > + if (!refcount_read(&map->refcnt)) > + return -EINVAL; > > - if (start == end) > - return 0; > + *start = overwrite ? head : old; > + *end = overwrite ? old : head; > > - size = end - start; > - if (size > (unsigned long)(md->mask) + 1) { > + if (*start == *end) > + return -EAGAIN; > + > + size = *end - *start; > + if (size > (unsigned long)(map->mask) + 1) { > if (!overwrite) { > WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n"); >
I know you did not change this, but is this leg even possible in !overwrite mode? I think kernel will throw away the data, keep the head and wait for tail to be read by user..
jirka
> - md->prev = head; > - perf_mmap__consume(md, overwrite); > - return 0; > + map->prev = head; > + perf_mmap__consume(map, overwrite); > + return -EAGAIN;
SNIP
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