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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 082EBC10F0E for ; Sun, 7 Apr 2019 07:51:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6EF821738 for ; Sun, 7 Apr 2019 07:51:25 +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="m0YJQGRD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726366AbfDGHvZ (ORCPT ); Sun, 7 Apr 2019 03:51:25 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:35376 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726114AbfDGHvZ (ORCPT ); Sun, 7 Apr 2019 03:51:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=ZwPAuRwarno1qHU3/71DykSg1HdMD2lVJV4I2hDtuuQ=; b=m0YJQGRDjhVG3EMLdkPgJNxER UR1d9SdCeeioggL/Ll8ettjUrtlHdpn5zViBl0D6/OXx9fSIBO1ECEa6ox9lGC9K5txX29YRJ5XYl Wj0rx3Nxu9tcOnuURSiIQb6m88UJghXcE8ztdj+Igj7kpf1VbFh8Vjj7ku8zzfmOCXxyGrZWi+SZg tt5n1S0eJ/sYMpjA1SOz1H+fyqTe0N1VbkCAD8tV9/BYf8ZOY2CIRwaGpreul8PLYmaQT+LEFKeEL 5ONp9khnjfzepcsgbhTSVA7jq85kAj65Q1CqZetka4IimsFM40RHffn3JRtqurd7MOjFC/b/Nk+J3 3c6c27Rqw==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1hD2aJ-0005pN-NP; Sun, 07 Apr 2019 07:51:23 +0000 Date: Sun, 7 Apr 2019 00:51:23 -0700 From: Christoph Hellwig To: Keith Busch Cc: Jens Axboe , linux-block@vger.kernel.org, Bart Van Assche , linux-nvme@lists.infradead.org, Ming Lei , Keith Busch , Jianchao Wang , Keith Busch , Thomas Gleixner Subject: Re: [PATCH] blk-mq: Wait for for hctx requests on CPU unplug Message-ID: <20190407075123.GA22003@infradead.org> References: <20190405215920.27085-1-keith.busch@intel.com> <226503cd-53ac-902c-7944-b2748407b1d3@kernel.dk> <20190405223719.GC25081@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Apr 05, 2019 at 05:36:32PM -0600, Keith Busch wrote: > On Fri, Apr 5, 2019 at 5:04 PM Jens Axboe wrote: > > Looking at current peak testing, I've got around 1.2% in queue enter > > and exit. It's definitely not free, hence my question. Probably safe > > to assume that we'll double that cycle counter, per IO. > > Okay, that's not negligible at all. I don't know of a faster reference > than the percpu_ref, but that much overhead would have to rule out > having a per hctx counter. Can we just replace queue_enter/exit with the per-hctx reference entirely?