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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 02668C43603 for ; Wed, 18 Dec 2019 09:51:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C851120717 for ; Wed, 18 Dec 2019 09:51:37 +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="TucDaIm+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725955AbfLRJvh (ORCPT ); Wed, 18 Dec 2019 04:51:37 -0500 Received: from merlin.infradead.org ([205.233.59.134]:35050 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725828AbfLRJvh (ORCPT ); Wed, 18 Dec 2019 04:51:37 -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=CCYsTiKmLFf9CmOEzk5lgJx0OEGqguLyDzTVud+iGeA=; b=TucDaIm+ISUWU5BpkawY63Sb3 SJ9SWk9Pu7f2dafCRqmUyN1UDC0w4kLQTiN7ACWPV22SKSosG2JeNzQElk7s4wDWElgtDN43Pu3Xs rgKJEYCbDoYbJObPK03ZeFF0p1VjonN6AyqIxvArc3Uh6MaYeiUzmHTRev4x8o1yRMSdDNe5l7PXU iT9AlSg8sP/UTe+q5TnbqfZ6ZBgMaKbcJ2XmfRB5wfEKx3+h7keMutdUIEhY7YAF9rQEq19Rk2W10 m2UIYcY37jmJT4elzwPg/t0rAFoteeDnVyns2y1aCLzL+ZhYyumgETnqOsEuTTloMoiggMq44kzI3 +YKxUJ5nQ==; 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 1ihVyx-0001FP-98; Wed, 18 Dec 2019 09:51:03 +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 36B023007F2; Wed, 18 Dec 2019 10:49:38 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 1966B2B3E30FC; Wed, 18 Dec 2019 10:51:01 +0100 (CET) Date: Wed, 18 Dec 2019 10:51:01 +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: <20191218095101.GQ2844@hirez.programming.kicks-ass.net> References: <20191218071942.22336-1-ming.lei@redhat.com> <20191218071942.22336-2-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191218071942.22336-2-ming.lei@redhat.com> 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 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. > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 90e4b00ace89..03e2e3c36067 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -219,6 +219,11 @@ void update_rq_clock(struct rq *rq) > update_rq_clock_task(rq, delta); > } > > +u64 sched_local_rq_clock(void) > +{ > + return this_rq()->clock; > +} > +EXPORT_SYMBOL_GPL(sched_local_rq_clock); Also, more NAK, you're exporting a variant of __rq_clock_broken(). (which, now that I git-grep for it, has become unused, good!)