From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62140C433F5 for ; Mon, 29 Nov 2021 06:24:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239677AbhK2G10 (ORCPT ); Mon, 29 Nov 2021 01:27:26 -0500 Received: from szxga08-in.huawei.com ([45.249.212.255]:28117 "EHLO szxga08-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233394AbhK2GZ0 (ORCPT ); Mon, 29 Nov 2021 01:25:26 -0500 Received: from dggemv703-chm.china.huawei.com (unknown [172.30.72.56]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4J2Zv52QtDz1DJ4s; Mon, 29 Nov 2021 14:19:29 +0800 (CST) Received: from kwepemm600019.china.huawei.com (7.193.23.64) by dggemv703-chm.china.huawei.com (10.3.19.46) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Mon, 29 Nov 2021 14:22:07 +0800 Received: from [10.174.177.210] (10.174.177.210) by kwepemm600019.china.huawei.com (7.193.23.64) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Mon, 29 Nov 2021 14:22:07 +0800 Subject: Re: [PATCH] pipe: remove needless spin_lock in pipe_read/pipe_write From: yangerkun To: , CC: References: <20211122041135.2450220-1-yangerkun@huawei.com> Message-ID: <22dd76ec-a50d-a2f1-8001-2a86de1d50c0@huawei.com> Date: Mon, 29 Nov 2021 14:22:06 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20211122041135.2450220-1-yangerkun@huawei.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.210] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemm600019.china.huawei.com (7.193.23.64) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org ping On 2021/11/22 12:11, yangerkun wrote: > Once enable CONFIG_WATCH_QUEUE, we should protect pipe with > pipe->rd_wait.lock since post_one_notification may write pipe from > contexts where pipe->mutex cannot be token. But nowdays we will try > take it for anycase, it seems needless. Besides, pipe_write will break > once it's pipe with O_NOTIFICATION_PIPE, pipe->rd_wait.lock seems no > need at all. We make some change base on that, and it can help improve > performance for some case like pipe_pst1 in libMicro. > > ARMv7 for our scene, before this patch: > 5483 nsecs/call > After this patch: > 4854 nsecs/call > > Signed-off-by: yangerkun > --- > fs/pipe.c | 15 +++++++-------- > 1 file changed, 7 insertions(+), 8 deletions(-) > > diff --git a/fs/pipe.c b/fs/pipe.c > index 6d4342bad9f1..e8ced0c50824 100644 > --- a/fs/pipe.c > +++ b/fs/pipe.c > @@ -320,14 +320,18 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) > > if (!buf->len) { > pipe_buf_release(pipe, buf); > - spin_lock_irq(&pipe->rd_wait.lock); > #ifdef CONFIG_WATCH_QUEUE > + if (pipe->watch_queue) > + spin_lock_irq(&pipe->rd_wait.lock); > if (buf->flags & PIPE_BUF_FLAG_LOSS) > pipe->note_loss = true; > #endif > tail++; > pipe->tail = tail; > - spin_unlock_irq(&pipe->rd_wait.lock); > +#ifdef CONFIG_WATCH_QUEUE > + if (pipe->watch_queue) > + spin_unlock_irq(&pipe->rd_wait.lock); > +#endif > } > total_len -= chars; > if (!total_len) > @@ -504,16 +508,11 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) > * it, either the reader will consume it or it'll still > * be there for the next write. > */ > - spin_lock_irq(&pipe->rd_wait.lock); > - > head = pipe->head; > - if (pipe_full(head, pipe->tail, pipe->max_usage)) { > - spin_unlock_irq(&pipe->rd_wait.lock); > + if (pipe_full(head, pipe->tail, pipe->max_usage)) > continue; > - } > > pipe->head = head + 1; > - spin_unlock_irq(&pipe->rd_wait.lock); > > /* Insert it into the buffer array */ > buf = &pipe->bufs[head & mask]; >