From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D58821422C7; Mon, 29 Jul 2024 09:50:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722246653; cv=none; b=lQ0SFnyIlqYF/p4zWgpyZ+lQgurrCOhvWXIpwh6LYai2A/f5qzajS3UXSbbgcXyw1m/0WPvKS+iBBiBT7+x5VrTemudXaDDkc2bv2RyYYunezg4d/C8rHdRySZx7ZUKUBHSfWQHYG2ZY/aE60pMNwko9skvi4Fgynogn1hOHa1I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722246653; c=relaxed/simple; bh=vnBJjS/Nkhu1Zs0dAazWe/voq1rP6YchWhpCNKQVKhs=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=fGUSkVwsKJtE1V6rTtC2SfwMcZEBEYDDWbFyt6OLzvHjao0sLaohQ446doZ+pGHih4iBrPzWa+Eg4KHpXe+rzmDC92g6UHf9HoEGpxisTNQ2A/SKCMvM37ZVanmkY3Gbegt8QscW9QFbtVBq34dHNDpbMqazDXTBo+juwSP9r/E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8D0E81007; Mon, 29 Jul 2024 02:51:15 -0700 (PDT) Received: from [10.57.78.240] (unknown [10.57.78.240]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5BBC63F64C; Mon, 29 Jul 2024 02:50:48 -0700 (PDT) Message-ID: <2cbb3467-1b49-4c86-9fad-9c75ce7d9c8f@arm.com> Date: Mon, 29 Jul 2024 11:50:40 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] sched/fair: Use all little CPUs for CPU-bound workload From: Pierre Gondois To: stable@vger.kernel.org, Sasha Levin , Lukasz Luba Cc: linux-kernel@vger.kernel.org, Qais Yousef , Vincent Guittot , Dietmar Eggemann , Ingo Molnar , Peter Zijlstra References: <20231206090043.634697-1-pierre.gondois@arm.com> <999a6c1d-c21d-4d16-a2a2-6d0b6e7df9a5@arm.com> Content-Language: en-US In-Reply-To: <999a6c1d-c21d-4d16-a2a2-6d0b6e7df9a5@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hello Sasha, Would it be possible to pick this patch for the 6.1 stable branch ? Or is there something I should do for this purpose ? Regards, Pierre On 6/25/24 15:25, Pierre Gondois wrote: > Hello stable folk, > > This patch was merged as: > commit 3af7524b1419 ("sched/fair: Use all little CPUs for CPU-bound workloads") > into 6.7, improving the following: > commit 0b0695f2b34a ("sched/fair: Rework load_balance()") > > Would it be possible to port it to the 6.1 stable branch ? > The patch should apply cleanly by cherry-picking onto v6.1.94, > > Regards, > Pierre > > > On 12/6/23 10:00, Pierre Gondois wrote: >> Running n CPU-bound tasks on an n CPUs platform: >> - with asymmetric CPU capacity >> - not being a DynamIq system (i.e. having a PKG level sched domain >> without the SD_SHARE_PKG_RESOURCES flag set) >> might result in a task placement where two tasks run on a big CPU >> and none on a little CPU. This placement could be more optimal by >> using all CPUs. >> >> Testing platform: >> Juno-r2: >> - 2 big CPUs (1-2), maximum capacity of 1024 >> - 4 little CPUs (0,3-5), maximum capacity of 383 >> >> Testing workload ([1]): >> Spawn 6 CPU-bound tasks. During the first 100ms (step 1), each tasks >> is affine to a CPU, except for: >> - one little CPU which is left idle. >> - one big CPU which has 2 tasks affine. >> After the 100ms (step 2), remove the cpumask affinity. >> >> Before patch: >> During step 2, the load balancer running from the idle CPU tags sched >> domains as: >> - little CPUs: 'group_has_spare'. Cf. group_has_capacity() and >> group_is_overloaded(), 3 CPU-bound tasks run on a 4 CPUs >> sched-domain, and the idle CPU provides enough spare capacity >> regarding the imbalance_pct >> - big CPUs: 'group_overloaded'. Indeed, 3 tasks run on a 2 CPUs >> sched-domain, so the following path is used: >> group_is_overloaded() >> \-if (sgs->sum_nr_running <= sgs->group_weight) return true; >> >> The following path which would change the migration type to >> 'migrate_task' is not taken: >> calculate_imbalance() >> \-if (env->idle != CPU_NOT_IDLE && env->imbalance == 0) >> as the local group has some spare capacity, so the imbalance >> is not 0. >> >> The migration type requested is 'migrate_util' and the busiest >> runqueue is the big CPU's runqueue having 2 tasks (each having a >> utilization of 512). The idle little CPU cannot pull one of these >> task as its capacity is too small for the task. The following path >> is used: >> detach_tasks() >> \-case migrate_util: >> \-if (util > env->imbalance) goto next; >> >> After patch: >> As the number of failed balancing attempts grows (with >> 'nr_balance_failed'), progressively make it easier to migrate >> a big task to the idling little CPU. A similar mechanism is >> used for the 'migrate_load' migration type. >> >> Improvement: >> Running the testing workload [1] with the step 2 representing >> a ~10s load for a big CPU: >> Before patch: ~19.3s >> After patch: ~18s (-6.7%) >> >> Similar issue reported at: >> https://lore.kernel.org/lkml/20230716014125.139577-1-qyousef@layalina.io/ >> >> v1: >> https://lore.kernel.org/all/20231110125902.2152380-1-pierre.gondois@arm.com/ >> v2: >> https://lore.kernel.org/all/20231124153323.3202444-1-pierre.gondois@arm.com/ >> >> Suggested-by: Vincent Guittot >> Signed-off-by: Pierre Gondois >> Reviewed-by: Vincent Guittot >> Reviewed-by: Dietmar Eggemann >> --- >> >> Notes: >> v2: >> - Used Vincent's approach. >> v3: >> - Updated commit message. >> - Added Reviewed-by tags >> >> kernel/sched/fair.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index d7a3c63a2171..9481b8cff31b 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -9060,7 +9060,7 @@ static int detach_tasks(struct lb_env *env) >> case migrate_util: >> util = task_util_est(p); >> >> - if (util > env->imbalance) >> + if (shr_bound(util, env->sd->nr_balance_failed) > env->imbalance) >> goto next; >> >> env->imbalance -= util; >