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 7451120897E for ; Mon, 2 Dec 2024 14:56:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733151377; cv=none; b=F7qwoGs5KJyQO5Dy+qV3aMAg47ErS3wfYB06COhAXgMpah8gxUvttcu8EKO/Z3ceBtrErjqgCU/2Y0tBxRc0Yeae9fg//z/o1/dIp2f2T+JoUiu+hA/txPMRhaXwCdF8cdfdj/x1ZJWuv+IlQG6WHyn6fwaeBDdQ9oD9uT9Yq10= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733151377; c=relaxed/simple; bh=EC9E0hucXqDeFyn5BpO7Ofdsa5Yur7No7rg1GgbSVN4=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References: Content-Type:MIME-Version; b=JBr4oYc+I7RVF4WkyPZs2OXf8OUsMETrKtzHO7tCQYfmVlbftEAw705Z6uo5xBBKOBR55xRmp7J4amxzwk0c24hlBcEZvX3UIJUkl6VmnSxhJwaFxIaRhqicIswrrO+7DGueGVK0fmgZqmV1qwQBu7c1sUYDkOZ2L3AclQB3TZQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=MzuhHVLr; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MzuhHVLr" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1733151374; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=EC9E0hucXqDeFyn5BpO7Ofdsa5Yur7No7rg1GgbSVN4=; b=MzuhHVLrkC6udHcaF8aUsxW+LwFTnzAeTAwiplE7NotVnD5JlAL7Gn9dAMmqU85HnzaTOI k2nSOYyvAWa3WUoFtCOjSRcSwLXtZmnlQMwUqK/EAKtABV/t2GnmgnN1hPfBRAPEu5nRhz zmF9h8Iqlt0LYPWhnu9/vPB0sC8vwRc= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-435-ZjfcfushOkGLR3RqI5_w4g-1; Mon, 02 Dec 2024 09:56:11 -0500 X-MC-Unique: ZjfcfushOkGLR3RqI5_w4g-1 X-Mimecast-MFC-AGG-ID: ZjfcfushOkGLR3RqI5_w4g Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-385e3cbf308so757313f8f.2 for ; Mon, 02 Dec 2024 06:56:11 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1733151370; x=1733756170; h=mime-version:user-agent:content-transfer-encoding:autocrypt :references:in-reply-to:date:to:from:subject:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=EC9E0hucXqDeFyn5BpO7Ofdsa5Yur7No7rg1GgbSVN4=; b=hNwsC/iZG60+1Zq3PLsh6f4QZpkkQKsktdefY5eEpJOlGgMlmI65wc9JpKIWSlTRub P4gpIPWMv8rnuRKyN2rUjm2vaF9+9dqOTxnNlCdPWpkR8WdJntWb8yCgXFiopoBmvZ6e DMFJndRWFOio6ab6km/jnvBPDtAFNYiSnhFs6Zv+Emi4LHsW+dcfLr/piK0tEM+ibqoI 2cCEKqbFSkStHCMTAzIsy3+HtHkMEmt9W/iUJQxuntpra7MLd2RboAY+RUILNEqFKxDf VTCg+U7NlOnAfF7W2tZ/KrSo080+Jh20n06rwetkgTmgeym3TpBB7atUXam1t/IaZDhX RwXg== X-Forwarded-Encrypted: i=1; AJvYcCXNq2c3tIC1+I1oh7Y/Vn0Yj6RH0YvTqNgkx4ME+On6Nliv4sgIUWaNIjX40rXeRhXb/ZSIpgMmN1XvsTo=@vger.kernel.org X-Gm-Message-State: AOJu0Yw9xheAIHP/Tm/sqRB+7E655E8O+Xucx9FTPaINAj8kYT741myc O+GT0EmKeMKBfAk5IXJa6YhhTEgQEL8RjfimqN3BUYDdTUVTbDTGnTDr5a8DMgzhViYK1LCtk15 1QiAISaV7OPJobFXhZzptrGDbvSjPCZpPefd8Y2qdS4eOm8Hc7LejsAWCfznwvA== X-Gm-Gg: ASbGnctp4JawjifD8SELnxciWNPhUm70Pi9G310t83LM93DT50ySdDYN4keA20DGpBb ScCxaDHuWJy81nm5vj49uo5+d3a4sfFyAkR5FuK3St1RnC+YQAfpf+jShtYrEZqMET42ho74Nbx H/ioGiHXq0MTjisQi2N9nqqBOS3kGCtqVsPDA8/mP50K7Eji84uZKJNN91Pl0n8d1ZpwHTTbFdA a2WbBEoVwHJ+6q1XNSURzsZ9qR2i90rQAQZqWapeaMjai4iKXbyed/jjBl9Y/WHjPlffTmAhSLw X-Received: by 2002:a5d:6d8d:0:b0:385:fa3d:19c6 with SMTP id ffacd0b85a97d-385fa3d251emr704877f8f.38.1733151370101; Mon, 02 Dec 2024 06:56:10 -0800 (PST) X-Google-Smtp-Source: AGHT+IG4l2XzqaYesgO1NND1lzztg36U2ZwkoTvJXF1I8fX5jH8ArXuN8EINJo3EoG8nWvxIoMzq/A== X-Received: by 2002:a5d:6d8d:0:b0:385:fa3d:19c6 with SMTP id ffacd0b85a97d-385fa3d251emr704857f8f.38.1733151369779; Mon, 02 Dec 2024 06:56:09 -0800 (PST) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([185.107.56.42]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-385e30c54bfsm7614208f8f.110.2024.12.02.06.56.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Dec 2024 06:56:09 -0800 (PST) Message-ID: <6b7b30528893b091b21a06ead610709219cd9ba0.camel@redhat.com> Subject: Re: [PATCH 1/2] sched: Optimise task_mm_cid_work duration From: Gabriele Monaco To: Mathieu Desnoyers , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , linux-kernel@vger.kernel.org Date: Mon, 02 Dec 2024 15:56:07 +0100 In-Reply-To: References: <20241202140735.56368-1-gmonaco@redhat.com> <20241202140735.56368-2-gmonaco@redhat.com> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0ByZWRoYXQuY29tPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmbiuWMCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfJzZgD/TXjnqCyqaZH/Y2w+YVbvm93WX2eqBqiVZ6VEjTuGNs8A/iPrKbzdWC7AicnK xyhmqeUWOzFx5P43S1E1dhsrLWgP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.2 (3.54.2-1.fc41) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Hi Mathieu, thanks for the quick reply. > Thanks for looking into this. I understand that you are after > minimizing the > latency introduced by task_mm_cid_work on isolated cores. I think > we'll need > to think a bit harder, because the proposed solution does not work: >=20 > =C2=A0 * for_each_cpu_from - iterate over CPUs present in @mask, from @cp= u > to the end of @mask. >=20 > cpu is uninitialized. So this is completely broken.=C2=A0 My bad, wrong macro.. Should be for_each_cpu > Was this tested > against a workload that actually uses concurrency IDs to ensure it > does > not break the whole thing ? Did you run the rseq selftests ? >=20 I did run the stress-ng --rseq command for a while and didn't see any error reported, but it's probably not bulletproof. I'll use the selftests for the next iterations. > Also, the mm_cidmask is a mask of concurrency IDs, not a mask of > CPUs. So > using it to iterate on CPUs is wrong. >=20 Mmh I get it, during my tests I was definitely getting better results than using the mm_cpus_allowed mask, but I guess that was a broken test so it just doesn't count.. Do you think using mm_cpus_allowed would make more sense, with the /risk/ of being a bit over-cautious? Gabriele