From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 21F2E538D for ; Thu, 26 Jan 2023 21:01:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674766878; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ntu39X9r3vWW6dw/7k9yhEgXDqdXpZhG83Nr+G649/c=; b=FDQ9ujKqsfZbSK0a0KNU/IZzds7VON423/oO85XWjdfsQ6egth78jZBkksuhSSjDRsuxqU 4EnkbUgjH1T3e82ysDPVZVErI5yAH0/TzY2yQxaxo5+5cLie3xrlk3Z4VUdEj1a4SYBBSR MXZRnPGrH84KpMoY729tPvinY6Ob+fg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-139-B9SODiOcNTeCqMyBZHzdUg-1; Thu, 26 Jan 2023 16:00:40 -0500 X-MC-Unique: B9SODiOcNTeCqMyBZHzdUg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4C03F857F82; Thu, 26 Jan 2023 20:58:42 +0000 (UTC) Received: from [10.22.33.13] (unknown [10.22.33.13]) by smtp.corp.redhat.com (Postfix) with ESMTP id 91575401530F; Thu, 26 Jan 2023 20:58:41 +0000 (UTC) Message-ID: <9861c077-55c6-60f4-02ea-bd0138945c16@redhat.com> Date: Thu, 26 Jan 2023 15:58:41 -0500 Precedence: bulk X-Mailing-List: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH v2] sched: Store restrict_cpus_allowed_ptr() call state Content-Language: en-US From: Waiman Long To: Will Deacon Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , Phil Auld , Linus Torvalds , linux-kernel@vger.kernel.org, regressions@lists.linux.dev, regressions@leemhuis.info References: <20230121021749.55313-1-longman@redhat.com> <20230124194805.GA27257@willie-the-truck> <20230126161110.GB29438@willie-the-truck> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 On 1/26/23 15:49, Waiman Long wrote: > On 1/26/23 11:11, Will Deacon wrote: >> On Tue, Jan 24, 2023 at 03:24:36PM -0500, Waiman Long wrote: >>> On 1/24/23 14:48, Will Deacon wrote: >>>> On Fri, Jan 20, 2023 at 09:17:49PM -0500, Waiman Long wrote: >>>>> The user_cpus_ptr field was originally added by commit b90ca8badbd1 >>>>> ("sched: Introduce task_struct::user_cpus_ptr to track requested >>>>> affinity"). It was used only by arm64 arch due to possible asymmetric >>>>> CPU setup. >>>>> >>>>> Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested >>>>> cpumask"), task_struct::user_cpus_ptr is repurposed to store user >>>>> requested cpu affinity specified in the sched_setaffinity(). >>>>> >>>>> This results in a performance regression in an arm64 system when >>>>> booted >>>>> with "allow_mismatched_32bit_el0" on the command-line. The arch >>>>> code will >>>>> (amongst other things) calls force_compatible_cpus_allowed_ptr() and >>>>> relax_compatible_cpus_allowed_ptr() when exec()'ing a 32-bit or a >>>>> 64-bit >>>>> task respectively. Now a call to relax_compatible_cpus_allowed_ptr() >>>>> will always result in a __sched_setaffinity() call whether there is a >>>>> previous force_compatible_cpus_allowed_ptr() call or not. >>>> I'd argue it's more than just a performance regression -- the affinity >>>> masks are set incorrectly, which is a user visible thing >>>> (i.e. sched_getaffinity() gives unexpected values). >>> Can your elaborate a bit more on what you mean by getting unexpected >>> sched_getaffinity() results? You mean the result is wrong after a >>> relax_compatible_cpus_allowed_ptr(). Right? >> Yes, as in the original report. If, on a 4-CPU system, I do the >> following >> with v6.1 and "allow_mismatched_32bit_el0" on the kernel cmdline: >> >> # for c in `seq 1 3`; do echo 0 > >> /sys/devices/system/cpu/cpu$c/online; done >> # yes > /dev/null & >> [1] 334 >> # taskset -p 334 >> pid 334's current affinity mask: 1 >> # for c in `seq 1 3`; do echo 1 > >> /sys/devices/system/cpu/cpu$c/online; done >> # taskset -p 334 >> pid 334's current affinity mask: f >> >> but with v6.2-rc5 that last taskset invocation gives: >> >> pid 334's current affinity mask: 1 >> >> so, yes, the performance definitely regresses, but that's because the >> affinity mask is wrong! > > I see what you mean now. Hotplug doesn't work quite well now because > user_cpus_ptr has been repurposed to store the value set of > sched_setaffinity() but not the previous cpus_mask before > force_compatible_cpus_allowed_ptr(). > > One possible solution is to modify the hotplug related code to check > for the cpus_allowed_restricted, and if set, check > task_cpu_possible_mask() to see if the cpu can be added back to its > cpus_mask. I will take a further look at that later. Wait, I think the cpuset hotplug code should be able to restore the right cpumask since task_cpu_possible_mask() is used there. Is cpuset enabled? Does the test works without allow_mismatched_32bit_el0? I think there may be a bug somewhere. Cheers, Longman