From: Yunsheng Lin <linyunsheng@huawei.com>
To: <davem@davemloft.net>, <kuba@kernel.org>, <jasowang@redhat.com>,
<mst@redhat.com>
Cc: <brouer@redhat.com>, <paulmck@kernel.org>, <peterz@infradead.org>,
<will@kernel.org>, <shuah@kernel.org>,
<linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
<linux-kselftest@vger.kernel.org>, <linuxarm@openeuler.org>
Subject: [PATCH net-next v3 2/3] ptr_ring: move r->queue[] clearing after r->consumer_head updating
Date: Thu, 1 Jul 2021 20:26:41 +0800 [thread overview]
Message-ID: <1625142402-64945-3-git-send-email-linyunsheng@huawei.com> (raw)
In-Reply-To: <1625142402-64945-1-git-send-email-linyunsheng@huawei.com>
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%
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);
}
--
2.7.4
next prev parent reply other threads:[~2021-07-01 12:27 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-01 12:26 [PATCH net-next v3 0/3] add benchmark selftest and optimization for ptr_ring Yunsheng Lin
2021-07-01 12:26 ` [PATCH net-next v3 1/3] selftests/ptr_ring: add benchmark application " Yunsheng Lin
2021-07-02 6:43 ` Jason Wang
2021-07-02 8:17 ` Yunsheng Lin
2021-07-02 8:30 ` Michael S. Tsirkin
2021-07-02 8:46 ` Yunsheng Lin
2021-07-02 9:04 ` Jason Wang
2021-07-02 9:54 ` Yunsheng Lin
2021-07-02 14:18 ` Michael S. Tsirkin
2021-07-05 1:43 ` Yunsheng Lin
2021-07-02 14:16 ` Michael S. Tsirkin
2021-07-01 12:26 ` Yunsheng Lin [this message]
2021-07-02 6:45 ` [PATCH net-next v3 2/3] ptr_ring: move r->queue[] clearing after r->consumer_head updating Jason Wang
2021-07-02 8:40 ` [Linuxarm] " Yunsheng Lin
2021-07-01 12:26 ` [PATCH net-next v3 3/3] ptr_ring: add barrier to ensure the visiblity of r->queue[] Yunsheng Lin
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