lkml.org 
[lkml]   [2018]   [Jan]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH V3 02/12] perf mmap: factor out function to find ringbuffer position
    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

    \
     
     \ /
      Last update: 2018-01-14 23:23    [W:4.170 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site