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 69D11C6FD18 for ; Wed, 29 Mar 2023 19:22:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230302AbjC2TWr (ORCPT ); Wed, 29 Mar 2023 15:22:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229951AbjC2TWl (ORCPT ); Wed, 29 Mar 2023 15:22:41 -0400 Received: from mail-yw1-x1134.google.com (mail-yw1-x1134.google.com [IPv6:2607:f8b0:4864:20::1134]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B95CE12E for ; Wed, 29 Mar 2023 12:22:37 -0700 (PDT) Received: by mail-yw1-x1134.google.com with SMTP id 00721157ae682-54601d90118so156650597b3.12 for ; Wed, 29 Mar 2023 12:22:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1680117757; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to; bh=MD5vx/bj0saF4TqNG1nIF/YU28Jg42gUeejN+X2NCpY=; b=jT/j7PjxyG20P2CKl37aHA/z29PlP5r8hnouR7V1cEBZfIyQle/ffgyZ7SeY8TFDTN LriKUchyJMzRZTZfx2Ra1tFVLAY+IMhcDrjzjdXPhFcyX9wQ7Iq+ch1Lp8XCUn+PP+XT mDo99xFXTYufeJOx6O5lkcrR1KnrVe7fdgkK5wdj2U9WZ56B4j+7MKNJrYUu3YvPOJMS ddD10ubhfVeY9zNjMGsO05U3lUzlkLtHm4GWbA1tvIzVEXeRefinLhNUJ5Dyd+qyBevy Xp/QTExSKgMNuwRvOPQ7LHvWnn4acK885eIH7mW88e7D4Z3v4p2DeFo9+nXpGm8NXh8t I/VA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680117757; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=MD5vx/bj0saF4TqNG1nIF/YU28Jg42gUeejN+X2NCpY=; b=rc+pH/JbqwUEUNpSL6y1+ChkGUgg8sQnr9I98bqDuSEbIyjI3kFx04ZMsyFGZKq2rp WiOY7Q69d93rO/nipos037eZrL5vrUCPZbSZCFbyyF6y3egNwfCIxASd+81WDEzR34ml 5gF2qL4EDDPugRus4+YgwBZwWQxve+SFS6fUgjcryC60/mJ1k/fjvjAXUhutLPq0olDu 5tayGRL/xC8EYMY19XgrGZM1PYgXia4yzpse57Ns18o2qS3QO3vKN2wWzfcmYEoGR00l /Qsuz4V0swS0GitSJGwK5AseP6ZxQ/u0QmuC8JDQOKd9QhfxyjKyE44DL6D/sUmK+IAI GKtQ== X-Gm-Message-State: AAQBX9f62qQEnzoQc4MmapXv2qeo1mz57xKEZHy8uUQeNRtBWkRjri+/ 6L/WKWquci/q4SZgKHecjrUnZA== X-Google-Smtp-Source: AKy350aGXqku0wFHBwnbv0ayIqkfKZQbDVwnxlDtv6ud72FCuk4s6YtJqZ1NSL1cWoc/4AVWoTxyWQ== X-Received: by 2002:a81:920c:0:b0:52e:e095:3a00 with SMTP id j12-20020a81920c000000b0052ee0953a00mr21208691ywg.25.1680117756881; Wed, 29 Mar 2023 12:22:36 -0700 (PDT) Received: from ripple.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id d8-20020a81d808000000b00545a08184dcsm3092357ywj.108.2023.03.29.12.22.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Mar 2023 12:22:35 -0700 (PDT) Date: Wed, 29 Mar 2023 12:22:24 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Tejun Heo cc: Yosry Ahmed , Shakeel Butt , Josef Bacik , Jens Axboe , Zefan Li , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , Vasily Averin , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org Subject: Re: [RFC PATCH 1/7] cgroup: rstat: only disable interrupts for the percpu lock In-Reply-To: Message-ID: References: <20230323040037.2389095-1-yosryahmed@google.com> <20230323040037.2389095-2-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Hi Tejun, On Wed, 29 Mar 2023, Tejun Heo wrote: > On Mon, Mar 27, 2023 at 04:23:13PM -0700, Yosry Ahmed wrote: > > Tejun, if having the lock be non-irq is a non-starter for you, I can > > This is an actual hazard. We see in prod these unprotected locks causing > very big spikes in tail latencies and they can be tricky to root cause too > and given the way rstat lock is used it's highly likely to be involved in > those scenarios with the proposed change, so it's gonna be a nack from my > end. Butting in here, I'm fascinated. This is certainly not my area, I know nothing about rstat, but this is the first time I ever heard someone arguing for more disabling of interrupts rather than less. An interrupt coming in while holding a contended resource can certainly add to latencies, that I accept of course. But until now, I thought it was agreed best practice to disable irqs only regretfully, when strictly necessary. If that has changed, I for one want to know about it. How should we now judge which spinlocks should disable interrupts and which should not? Page table locks are currently my main interest - should those be changed? Thanks, Hugh