From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============7716241726980557597==" MIME-Version: 1.0 From: Christoph Hellwig To: lkp@lists.01.org Subject: Re: [lkp-robot] [fs] 3deb642f0d: will-it-scale.per_process_ops -8.8% regression Date: Fri, 22 Jun 2018 13:53:00 +0200 Message-ID: <20180622115300.GA14654@lst.de> In-Reply-To: <20180622110117.GU30522@ZenIV.linux.org.uk> List-Id: --===============7716241726980557597== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Fri, Jun 22, 2018 at 12:01:17PM +0100, Al Viro wrote: > For fuck sake, if you want vfs_poll() inlined, *make* *it* *inlined*. That is not going to help with de-virtualizing _qproc, which was the whole idea of that change. At least not without a compiler way smarter than gcc. But if you want it inline that is fine with me, it just seems little large for inlining. None that I plan to actually remove all calls except for poll and select for vfs_poll in a pending series, at which point it would become static anyway. > Said that, you are not attacking the worst part of it - it's a static > branch, not the considerably more costly indirect ones. Remember when > I asked you about the price of those? Method calls are costly. And back then it did not show up even in poll heavy workloads. But since then something new happened - spectre mitigations, which make indirect calls exorbitantly more expensive. > Now, ->sk_wq is modified only in sock_init_data() and sock_graft(); > the latter, IIRC, is ->accept() helper. Do we ever call either of > those on a sock of already opened file? IOW, is there any real > reason for socket ->get_poll_head() not to be constant, other > than wanting to keep POLL_BUSY_LOOP handling out of ->poll_mask()? > I agree that POLL_BUSY_LOOP is ugly as hell, but you *still* have > sock_poll_mask() not free from it... I'd have to defer to networking folks if busy looping after pollwait is what they want, but I suspect the answer is no, by the time we are already waiting for the queue busy waiting seems pointless. --===============7716241726980557597==-- 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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 DD52CC43142 for ; Fri, 22 Jun 2018 11:43:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9686A23C2A for ; Fri, 22 Jun 2018 11:43:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9686A23C2A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751478AbeFVLnh (ORCPT ); Fri, 22 Jun 2018 07:43:37 -0400 Received: from verein.lst.de ([213.95.11.211]:56150 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751210AbeFVLnf (ORCPT ); Fri, 22 Jun 2018 07:43:35 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id BE90C68E45; Fri, 22 Jun 2018 13:53:00 +0200 (CEST) Date: Fri, 22 Jun 2018 13:53:00 +0200 From: Christoph Hellwig To: Al Viro Cc: Christoph Hellwig , Linus Torvalds , kernel test robot , Greg Kroah-Hartman , "Darrick J. Wong" , Linux Kernel Mailing List , LKP Subject: Re: [lkp-robot] [fs] 3deb642f0d: will-it-scale.per_process_ops -8.8% regression Message-ID: <20180622115300.GA14654@lst.de> References: <20180622082752.GX11011@yexl-desktop> <20180622095608.GA12263@lst.de> <20180622100014.GA12425@lst.de> <20180622110117.GU30522@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180622110117.GU30522@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 22, 2018 at 12:01:17PM +0100, Al Viro wrote: > For fuck sake, if you want vfs_poll() inlined, *make* *it* *inlined*. That is not going to help with de-virtualizing _qproc, which was the whole idea of that change. At least not without a compiler way smarter than gcc. But if you want it inline that is fine with me, it just seems little large for inlining. None that I plan to actually remove all calls except for poll and select for vfs_poll in a pending series, at which point it would become static anyway. > Said that, you are not attacking the worst part of it - it's a static > branch, not the considerably more costly indirect ones. Remember when > I asked you about the price of those? Method calls are costly. And back then it did not show up even in poll heavy workloads. But since then something new happened - spectre mitigations, which make indirect calls exorbitantly more expensive. > Now, ->sk_wq is modified only in sock_init_data() and sock_graft(); > the latter, IIRC, is ->accept() helper. Do we ever call either of > those on a sock of already opened file? IOW, is there any real > reason for socket ->get_poll_head() not to be constant, other > than wanting to keep POLL_BUSY_LOOP handling out of ->poll_mask()? > I agree that POLL_BUSY_LOOP is ugly as hell, but you *still* have > sock_poll_mask() not free from it... I'd have to defer to networking folks if busy looping after pollwait is what they want, but I suspect the answer is no, by the time we are already waiting for the queue busy waiting seems pointless.