lkml.org 
[lkml]   [2021]   [Jul]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH net-next v3 2/3] ptr_ring: move r->queue[] clearing after r->consumer_head updating
    From
    Date

    在 2021/7/1 下午8:26, Yunsheng Lin 写道:
    > Currently r->queue[] clearing is done before r->consumer_head
    > updating, which makes the __ptr_ring_empty() returning false
    > positive result(the ring is non-empty, but __ptr_ring_empty()
    > suggest that it is empty) if the checking is done after the
    > r->queue clearing and before the consumer_head moving forward.
    >
    > Move the r->queue[] clearing after consumer_head moving forward
    > to avoid the above case.
    >
    > As a side effect of above change, a consumer_head checking is
    > avoided for the likely case, and it has noticeable performance
    > improvement when it is tested using the ptr_ring_test selftest
    > added in the previous patch.
    >
    > Tested using the "perf stat -r 1000 ./ptr_ring_test -s 1000 -m 1
    > -N 100000000", comparing the elapsed time:
    >
    > arch unpatched patched improvement
    > arm64 2.087205 sec 1.888224 sec +9.5%
    > X86 2.6538 sec 2.5422 sec +4.2%


    I think we need the number of real workloads here.

    Thanks


    >
    > Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
    > ---
    > V3: adjust the title and comment log according to disscusion in
    > V2, and update performance data using "perf stat -r".
    > V2: Add performance data.
    > ---
    > include/linux/ptr_ring.h | 25 ++++++++++++++++---------
    > 1 file changed, 16 insertions(+), 9 deletions(-)
    >
    > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
    > index 808f9d3..db9c282 100644
    > --- a/include/linux/ptr_ring.h
    > +++ b/include/linux/ptr_ring.h
    > @@ -261,8 +261,7 @@ static inline void __ptr_ring_discard_one(struct ptr_ring *r)
    > /* Note: we must keep consumer_head valid at all times for __ptr_ring_empty
    > * to work correctly.
    > */
    > - int consumer_head = r->consumer_head;
    > - int head = consumer_head++;
    > + int consumer_head = r->consumer_head + 1;
    >
    > /* Once we have processed enough entries invalidate them in
    > * the ring all at once so producer can reuse their space in the ring.
    > @@ -271,19 +270,27 @@ static inline void __ptr_ring_discard_one(struct ptr_ring *r)
    > */
    > if (unlikely(consumer_head - r->consumer_tail >= r->batch ||
    > consumer_head >= r->size)) {
    > + int tail = r->consumer_tail;
    > +
    > + if (unlikely(consumer_head >= r->size)) {
    > + r->consumer_tail = 0;
    > + WRITE_ONCE(r->consumer_head, 0);
    > + } else {
    > + r->consumer_tail = consumer_head;
    > + WRITE_ONCE(r->consumer_head, consumer_head);
    > + }
    > +
    > /* Zero out entries in the reverse order: this way we touch the
    > * cache line that producer might currently be reading the last;
    > * producer won't make progress and touch other cache lines
    > * besides the first one until we write out all entries.
    > */
    > - while (likely(head >= r->consumer_tail))
    > - r->queue[head--] = NULL;
    > - r->consumer_tail = consumer_head;
    > - }
    > - if (unlikely(consumer_head >= r->size)) {
    > - consumer_head = 0;
    > - r->consumer_tail = 0;
    > + while (likely(--consumer_head >= tail))
    > + r->queue[consumer_head] = NULL;
    > +
    > + return;
    > }
    > +
    > /* matching READ_ONCE in __ptr_ring_empty for lockless tests */
    > WRITE_ONCE(r->consumer_head, consumer_head);
    > }

    \
     
     \ /
      Last update: 2021-07-02 08:46    [W:2.722 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site