From patchwork Thu Jul 1 12:26:41 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yunsheng Lin X-Patchwork-Id: 469844 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7CDA9C11F6B for ; Thu, 1 Jul 2021 12:27:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 63C3461407 for ; Thu, 1 Jul 2021 12:27:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236461AbhGAM3z (ORCPT ); Thu, 1 Jul 2021 08:29:55 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:9442 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236332AbhGAM3w (ORCPT ); Thu, 1 Jul 2021 08:29:52 -0400 Received: from dggemv711-chm.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4GFy7W35R8zZpSZ; Thu, 1 Jul 2021 20:24:07 +0800 (CST) Received: from dggpemm500005.china.huawei.com (7.185.36.74) by dggemv711-chm.china.huawei.com (10.1.198.66) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 1 Jul 2021 20:27:14 +0800 Received: from localhost.localdomain (10.69.192.56) by dggpemm500005.china.huawei.com (7.185.36.74) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 1 Jul 2021 20:27:14 +0800 From: Yunsheng Lin To: , , , CC: , , , , , , , , 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 Message-ID: <1625142402-64945-3-git-send-email-linyunsheng@huawei.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1625142402-64945-1-git-send-email-linyunsheng@huawei.com> References: <1625142402-64945-1-git-send-email-linyunsheng@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.69.192.56] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemm500005.china.huawei.com (7.185.36.74) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 --- 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); }