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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BB72AC433FE for ; Mon, 7 Dec 2020 16:09:24 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4FE1323741 for ; Mon, 7 Dec 2020 16:09:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4FE1323741 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BB5EC8D0003; Mon, 7 Dec 2020 11:09:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B673A8D0001; Mon, 7 Dec 2020 11:09:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A2EFB8D0003; Mon, 7 Dec 2020 11:09:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0028.hostedemail.com [216.40.44.28]) by kanga.kvack.org (Postfix) with ESMTP id 8BFE58D0001 for ; Mon, 7 Dec 2020 11:09:23 -0500 (EST) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 43190181AEF23 for ; Mon, 7 Dec 2020 16:09:23 +0000 (UTC) X-FDA: 77566971006.24.ghost51_3b10ec3273df Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin24.hostedemail.com (Postfix) with ESMTP id 2243A1A4A0 for ; Mon, 7 Dec 2020 16:09:23 +0000 (UTC) X-HE-Tag: ghost51_3b10ec3273df X-Filterd-Recvd-Size: 4393 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by imf16.hostedemail.com (Postfix) with ESMTP for ; Mon, 7 Dec 2020 16:09:21 +0000 (UTC) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1607357360; 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: in-reply-to:in-reply-to:references:references; bh=022gMNpDKo1YTcVrr7g7NDb6eEDzMx+ZJgQ/bHeb2qQ=; b=QOB+fZWx9qdPF9HIMMgOA0knHiX3uB4MO/SwRTeVbDTL5o2rJU5hgpVhvuLOs789wXgW+G ZZ4u91rivLr6A+jeuFMrN2b8yVTsYCZ+XySYDnt0iuFMgP3WX7AHc84FnDYtK+h4HvGnnu WMNyaNKACGI3AfGUMqMkF4gRydR1PFSTH85zcfI+WdtFA4ZBgiLsm4DGqzZdqH76cAAybF hL6JACIO0wtWmc8swbhHoYgAakD32J5uPGXLxpiuRWM7Te6B+0bxgRc/tiVVmPbrEF2Fs4 nhEk+xmKNWWum1I7MOx7BGOxSK8+qUB9LfUEdksHY1R0Fzs9aHROD5rYkN/ZeA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1607357360; 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: in-reply-to:in-reply-to:references:references; bh=022gMNpDKo1YTcVrr7g7NDb6eEDzMx+ZJgQ/bHeb2qQ=; b=IcnjF+zqPhe98TO7b4ZIHmZ1Lxn4n+rU11Z+y0HsM6FFI60WItHNONATP696BxOET4DkfB nix6nkjAPzQOGtBQ== To: Christoph Lameter Cc: Marcelo Tosatti , Matthew Wilcox , linux-mm@kvack.org, Andrew Morton , Alex Belits , Phil Auld , Frederic Weisbecker , Peter Zijlstra Subject: Re: [PATCH] mm: introduce sysctl file to flush per-cpu vmstat statistics In-Reply-To: References: <20201117162805.GA274911@fuller.cnet> <20201117180356.GT29991@casper.infradead.org> <20201117202317.GA282679@fuller.cnet> <20201127154845.GA9100@fuller.cnet> <87h7p4dwus.fsf@nanos.tec.linutronix.de> <87v9djd1db.fsf@nanos.tec.linutronix.de> Date: Mon, 07 Dec 2020 17:09:19 +0100 Message-ID: <87lfe961jk.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Dec 07 2020 at 08:08, Christoph Lameter wrote: > On Thu, 3 Dec 2020, Thomas Gleixner wrote: > Again saving data may not be possible through the kernel since syscalls > may have too much overhead and latency. > >> repeat the above... > > There is a fundamental misunderstanding here. This is not primarily about > compute but about I/O. In particular I/O that does not involve the kernel. > RDMA or things like DPDK, SPDK or other low hardware level things. The fundamental misunderstanding is that people just look at and care about their own turf. The above is valid in compute intensive workloads where the compute dominates the whole scenario. Not being disturbed there is a gain because of not losing cache locality due to interrupts, IPIs or whatever. >> Policy is not a binary on/off problem. It's manifold across all levels >> of the stack and only a kernel problem when it comes down to the last >> line of defence. > > This a clearly defined set of functions and I am not sure how policy fits > into that. It's about silencing different and largely independent parts of the OS on a particular CPU. Just defining upfront that there is only the choice of all or nothing _is_ policy. There is a very wide range of use case scenarios out there and just because the ones which you care about needs X does not mean that X is the right thing for everybody else. You still can have X and let other people define their own set of things they want to be protected against. Aside of that having it selectively is a plus for debugability, testing etc. All or nothing is always the worst choice if a more fine grained approach is possible with no big effort. Granted there are things where you only can say: all or nothing, but that's definitely not the case here. Thanks, tglx