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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 D5979C43603 for ; Thu, 19 Dec 2019 09:21:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A5DC0222C2 for ; Thu, 19 Dec 2019 09:21:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="mddEP1se" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726617AbfLSJVE (ORCPT ); Thu, 19 Dec 2019 04:21:04 -0500 Received: from merlin.infradead.org ([205.233.59.134]:44860 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726599AbfLSJVD (ORCPT ); Thu, 19 Dec 2019 04:21:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=L5GkT/t6f4PnNOvpHdWu3aKGL2zH/bo2tSmNC9/q9HA=; b=mddEP1seEEQAJCSWNeDGhge7a 1v9fDA9ktosw6z8UFtOF11Q7LsoUHivAylwsfp/MnLDAzmo2fs1DseTWKz1Kzp4rtHQd6L2psD4Nj 7dG8aKM6HeUTTsD15EMqCijzys4PmoKjOqAohFrQSRl78r70RtSwpGiBTaWB61TIrahAZnWozWdeH xFWuRZuIEboS1BBgCwUJCiUWVsRJgwdqi4bHrFtTnMbeXiCysahaT7x/vIdCkbhOG5qhEFmRZYzVc MVtAF6FdHkF6XtGdYo/k8m9KFMYnrcr+o2RIPAkA5yR71aq6UFerio/21v1RZFMyfcR4m4aNJEeJi Dd0fzC12g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1ihryx-0005Zr-Fv; Thu, 19 Dec 2019 09:20:31 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 9871A3007F2; Thu, 19 Dec 2019 10:19:03 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 06B162B291C41; Thu, 19 Dec 2019 10:20:27 +0100 (CET) Date: Thu, 19 Dec 2019 10:20:26 +0100 From: Peter Zijlstra To: Ming Lei Cc: Thomas Gleixner , Jens Axboe , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, Long Li , Ingo Molnar , Keith Busch , Christoph Hellwig , Sagi Grimberg , John Garry , Hannes Reinecke Subject: Re: [RFC PATCH 1/3] sched/core: add API for exporting runqueue clock Message-ID: <20191219092026.GW2844@hirez.programming.kicks-ass.net> References: <20191218071942.22336-1-ming.lei@redhat.com> <20191218071942.22336-2-ming.lei@redhat.com> <20191218095101.GQ2844@hirez.programming.kicks-ass.net> <20191219012914.GA6080@ming.t460p> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191219012914.GA6080@ming.t460p> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Dec 19, 2019 at 09:29:14AM +0800, Ming Lei wrote: > On Wed, Dec 18, 2019 at 10:51:01AM +0100, Peter Zijlstra wrote: > > On Wed, Dec 18, 2019 at 03:19:40PM +0800, Ming Lei wrote: > > > Scheduler runqueue maintains its own software clock that is periodically > > > synchronised with hardware. Export this clock so that it can be used > > > by interrupt flood detection for saving the cost of reading from hardware. > > > > But you don't have much, if any, guarantees the thing gets updated. > > Any software clock won't be guaranteed to be updated in time, however, > they are still useful. It still is broken, and I really don't want to expose this for whatever reason.