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 4CC90C43142 for ; Fri, 22 Jun 2018 12:30:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0D543241DC for ; Fri, 22 Jun 2018 12:30:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0D543241DC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ZenIV.linux.org.uk 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 S1751478AbeFVMaF (ORCPT ); Fri, 22 Jun 2018 08:30:05 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:32930 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751342AbeFVMaE (ORCPT ); Fri, 22 Jun 2018 08:30:04 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.87 #1 (Red Hat Linux)) id 1fWLCO-0008Bj-P8; Fri, 22 Jun 2018 12:29:56 +0000 Date: Fri, 22 Jun 2018 13:29:56 +0100 From: Al Viro To: Christoph Hellwig Cc: 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: <20180622122956.GX30522@ZenIV.linux.org.uk> References: <20180622082752.GX11011@yexl-desktop> <20180622095608.GA12263@lst.de> <20180622100014.GA12425@lst.de> <20180622110117.GU30522@ZenIV.linux.org.uk> <20180622115300.GA14654@lst.de> <20180622115613.GV30522@ZenIV.linux.org.uk> <20180622120739.GA15351@lst.de> <20180622121722.GW30522@ZenIV.linux.org.uk> <20180622123307.GA16699@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180622123307.GA16699@lst.de> User-Agent: Mutt/1.9.1 (2017-09-22) 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 02:33:07PM +0200, Christoph Hellwig wrote: > On Fri, Jun 22, 2018 at 01:17:22PM +0100, Al Viro wrote: > > > The problem is that call to sk_busy_loop(), which is going to be indirect > > > no matter what. > > > > if ->f_poll_head is NULL { > > use ->poll > > } else { > > if can ll_poll (checked in ->f_mode) > > call ->ll_poll(), if it returns what we want - we are done > > add to ->f_poll_head > > call ->poll_mask() > > What I have for now is slightly different: > > if ((events & POLL_BUSY_LOOP) && file->f_op->poll_busy_loop) > file->f_op->poll_busy_loop(file, events); > > if (file->f_op->poll) { > return file->f_op->poll(file, pt); > } else if (file_has_poll_mask(file)) { > ... > } > > returns whatever we want part is something I want to look into > once the basics are done as it probably is non entirely trivial due to > structure of polling in the low-level network protocol. First of all, you'll get the same ->f_op for *all* sockets. So you'll be hitting that path regardless of sk_can_busy_loop(sock->sk). What's more, that way you get (on fast path) even more indirect calls, AFAICS. And I don't see any point in separate file_has_poll_mask() - just check ->f_poll_head and that's it.