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 A0619C433F5 for ; Tue, 14 Dec 2021 17:28:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233853AbhLNR2I (ORCPT ); Tue, 14 Dec 2021 12:28:08 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:39692 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233789AbhLNR2H (ORCPT ); Tue, 14 Dec 2021 12:28:07 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 82E63B81BB9; Tue, 14 Dec 2021 17:28:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5553BC34604; Tue, 14 Dec 2021 17:28:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639502885; bh=iWhZUpZug7nx6pfIKr0DItc2+D2cy9/JIdFzbQtsEhI=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=rYv9JVZ9YX6Z0mBpVDMKm5mu/TzapluDlyLScme2UrTuIXRhZgJB+QO6JHt2eHkyY 3+Jqu7AOYi1QgWWEksD+65gGuD0VjAq1acIcvtuXXbqs+tH8BEhJowarrvQvSWSPCS 8kJvbqQpEEGu3nXWKmkGoYBqfMPTzpI/yorx8TTNlK8WkzYco3Cu1XxPzAxUGbcxsY iO+svhxl9Uio5GhrkOjfUMJ1zxy9eQVcWcj0E5w9TM/2/0tMICRAFO/Yhd+T1cWrb7 gJ3bLGn7U40/JibUXtbMYNVionNiTEfCchB2L6TzUJibY8OBopc2EEs98X8fh7TMjS l3SaS41aVL9JQ== Received: by mail-yb1-f180.google.com with SMTP id d10so48128844ybe.3; Tue, 14 Dec 2021 09:28:05 -0800 (PST) X-Gm-Message-State: AOAM530j4MZ4wwlvdqpMAD0OIlKF4S3mrXfdpeDpk1u9t+t3reWEPLgJ 05JFBUiN2cHil5aUB3xrTVjkaylQzmD5FUbWWUY= X-Google-Smtp-Source: ABdhPJzaIWhZ2KXfV3WBSipGqRCpcplKqZGV0U2L1BO8aObP0RNronSXvgKpJlPOO1T9RuBg8PP4FeHUtdss6/yaXVI= X-Received: by 2002:a25:8284:: with SMTP id r4mr383980ybk.47.1639502884465; Tue, 14 Dec 2021 09:28:04 -0800 (PST) MIME-Version: 1.0 References: <20211214031553.16435-1-yajun.deng@linux.dev> In-Reply-To: <20211214031553.16435-1-yajun.deng@linux.dev> From: Song Liu Date: Tue, 14 Dec 2021 09:27:53 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] lib/raid6: fix abnormally high latency To: Yajun Deng Cc: stockhausen@collogia.de, open list , linux-rt-users@vger.kernel.org, linux-raid Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On Mon, Dec 13, 2021 at 7:17 PM Yajun Deng wrote: > > We found an abnormally high latency when executing modprobe raid6_pq, the > latency is greater than 1.2s when CONFIG_PREEMPT_VOLUNTARY=y, greater than > 67ms when CONFIG_PREEMPT=y, and greater than 16ms when CONFIG_PREEMPT_RT=y. > This is caused by disable the preemption, this time is too long and > unreasonable. We just need to disable migration. so used migrate_disable()/ > migrate_enable() instead of preempt_disable()/preempt_enable(). This is > beneficial for CONFIG_PREEMPT=y or CONFIG_PREEMPT_RT=y, but no effect for > CONFIG_PREEMPT_VOLUNTARY=y. > > Fixes: fe5cbc6e06c7 ("md/raid6 algorithms: delta syndrome functions") > Signed-off-by: Yajun Deng We measure the speed of different RAID algorithms.If we don't disable preempt, the result may be inaccurate, right? IIUC, we only disable preempt for 16 jiffies. Why do we see 1.2 second delay? Thanks, Song > --- > lib/raid6/algos.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/lib/raid6/algos.c b/lib/raid6/algos.c > index 6d5e5000fdd7..21611d05c34c 100644 > --- a/lib/raid6/algos.c > +++ b/lib/raid6/algos.c > @@ -162,7 +162,7 @@ static inline const struct raid6_calls *raid6_choose_gen( > > perf = 0; > > - preempt_disable(); > + migrate_disable(); > j0 = jiffies; > while ((j1 = jiffies) == j0) > cpu_relax(); > @@ -171,7 +171,7 @@ static inline const struct raid6_calls *raid6_choose_gen( > (*algo)->gen_syndrome(disks, PAGE_SIZE, *dptrs); > perf++; > } > - preempt_enable(); > + migrate_enable(); > > if (perf > bestgenperf) { > bestgenperf = perf; > @@ -186,7 +186,7 @@ static inline const struct raid6_calls *raid6_choose_gen( > > perf = 0; > > - preempt_disable(); > + migrate_disable(); > j0 = jiffies; > while ((j1 = jiffies) == j0) > cpu_relax(); > @@ -196,7 +196,7 @@ static inline const struct raid6_calls *raid6_choose_gen( > PAGE_SIZE, *dptrs); > perf++; > } > - preempt_enable(); > + migrate_enable(); > > if (best == *algo) > bestxorperf = perf; > -- > 2.32.0 >