From patchwork Fri Dec 17 02:16:10 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yajun Deng X-Patchwork-Id: 525983 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 74CD7C433F5 for ; Fri, 17 Dec 2021 02:17:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230396AbhLQCRE (ORCPT ); Thu, 16 Dec 2021 21:17:04 -0500 Received: from out2.migadu.com ([188.165.223.204]:28507 "EHLO out2.migadu.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229733AbhLQCRE (ORCPT ); Thu, 16 Dec 2021 21:17:04 -0500 X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1639707422; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=uMigS+pNPz4JoxL7AW7Hx0wGyz7OYXv14jFz4Dq7WuY=; b=Fijp2w8r8Xl5FOxxfSDV4SzJxABMZHQZ4VUVTBwEb79z+NaI0wH1PAkmMmUgZO0uxs4NTF evlO1x+Upx2yRZecfE+3MPKrY7VcC/hNpSm/wkgX/KYXcFLhJs2T7nWB35Ip/LUOsJCa1J 8yobmWvguL17FEzgD/f4DcVzGc5e9CQ= From: Yajun Deng To: song@kernel.org Cc: masahiroy@kernel.org, williams@redhat.com, pmenzel@molgen.mpg.de, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, linux-raid@vger.kernel.org, stable@vger.kernel.org, Yajun Deng Subject: [PATCH v3] lib/raid6: Reduce high latency by using migrate instead of preempt Date: Fri, 17 Dec 2021 10:16:10 +0800 Message-Id: <20211217021610.12801-1-yajun.deng@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org 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. How to reproduce: - Install cyclictest sudo apt install rt-tests - Run cyclictest example in one terminal sudo cyclictest -S -p 95 -d 0 -i 1000 -D 24h -m - Modprobe raid6_pq in another terminal sudo modprobe raid6_pq This is caused by ksoftirqd fail to scheduled due to disable preemption, this time is too long and unreasonable. Reduce high latency by using migrate_disabl()/emigrate_enable() instead of preempt_disable()/preempt_enable(), the latency won't greater than 100us. This patch beneficial for CONFIG_PREEMPT=y or CONFIG_PREEMPT_RT=y, but no effect for CONFIG_PREEMPT_VOLUNTARY=y. Cc: stable@vger.kernel.org Fixes: fe5cbc6e06c7 ("md/raid6 algorithms: delta syndrome functions") Fixes: cc4589ebfae6 ("Rename raid6 files now they're in a 'raid6' directory.") Link: https://lore.kernel.org/linux-raid/b06c5e3ef3413f12a2c2b2a241005af9@linux.dev/T/#t # v1 Signed-off-by: Yajun Deng --- 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;