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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 3A2F0C3F2CD for ; Wed, 4 Mar 2020 15:22:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E79B2166E for ; Wed, 4 Mar 2020 15:22:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LPpRnl+H" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725765AbgCDPWz (ORCPT ); Wed, 4 Mar 2020 10:22:55 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:45311 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725795AbgCDPWz (ORCPT ); Wed, 4 Mar 2020 10:22:55 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583335373; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=eTaBFBZPc0pfImLCT+DWWsM1zO1I+2p7UGeVMcw2jEk=; b=LPpRnl+HXUq4mRnQUPxbaIXBJBLxThZf6OqDMAVoxIRqflqAmV8wAdHNPi0RmjNvazNGVA LuSeOQVcNMR9t2YD/5j9K2KM4DJJDYP39DyN9nAKu5mbKys/3mNd1SQfBWLmezWETFskvD fKwqnC0Sd1AHdbJMoomLg5Ep9BoWdcw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-350-aH2beAGrNZG6ypYcSKXG9g-1; Wed, 04 Mar 2020 10:22:50 -0500 X-MC-Unique: aH2beAGrNZG6ypYcSKXG9g-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E27C31005510; Wed, 4 Mar 2020 15:22:47 +0000 (UTC) Received: from ws.net.home (ovpn-204-202.brq.redhat.com [10.40.204.202]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7BE6991D7D; Wed, 4 Mar 2020 15:22:44 +0000 (UTC) Date: Wed, 4 Mar 2020 16:22:41 +0100 From: Karel Zak To: Ian Kent Cc: Greg Kroah-Hartman , Miklos Szeredi , David Howells , Christian Brauner , James Bottomley , Steven Whitehouse , Miklos Szeredi , viro , Christian Brauner , Jann Horn , "Darrick J. Wong" , Linux API , linux-fsdevel , lkml Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver #17] Message-ID: <20200304152241.iaiulvl5xisnuxp6@ws.net.home> References: <20200228155244.k4h4hz3dqhl7q7ks@wittgenstein> <107666.1582907766@warthog.procyon.org.uk> <0403cda7345e34c800eec8e2870a1917a8c07e5c.camel@themaw.net> <1509948.1583226773@warthog.procyon.org.uk> <20200303113814.rsqhljkch6tgorpu@ws.net.home> <20200303130347.GA2302029@kroah.com> <33d900c8061c40f70ba2b9d1855fd6bd1c2b68bb.camel@themaw.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33d900c8061c40f70ba2b9d1855fd6bd1c2b68bb.camel@themaw.net> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, Mar 04, 2020 at 10:01:33AM +0800, Ian Kent wrote: > On Tue, 2020-03-03 at 14:03 +0100, Greg Kroah-Hartman wrote: > > Actually, I like this idea (the syscall, not just the unlimited > > beers). > > Maybe this could make a lot of sense, I'll write some actual tests > > for > > it now that syscalls are getting "heavy" again due to CPU vendors > > finally paying the price for their madness... > > The problem isn't with open->read->close but with the mount info. > changing between reads (ie. seq file read takes and drops the > needed lock between reads at least once). readfile() is not reaction to mountinfo. The motivation is that we have many places with trivial open->read->close for very small text files due to /sys and /proc. The current way how kernel delivers these small strings to userspace seems pretty inefficient if we can do the same by one syscall. Karel $ strace -e openat,read,close -c ps aux ... % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 43.32 0.004190 4 987 read 31.42 0.003039 3 844 4 openat 25.26 0.002443 2 842 close ------ ----------- ----------- --------- --------- ---------------- 100.00 0.009672 2673 4 total $ strace -e openat,read,close -c lsns ... % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 39.95 0.001567 2 593 openat 30.93 0.001213 2 597 close 29.12 0.001142 3 365 read ------ ----------- ----------- --------- --------- ---------------- 100.00 0.003922 1555 total $ strace -e openat,read,close -c lscpu ... % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 44.67 0.001480 7 189 52 openat 34.77 0.001152 6 180 read 20.56 0.000681 4 140 close ------ ----------- ----------- --------- --------- ---------------- 100.00 0.003313 509 52 total -- Karel Zak http://karelzak.blogspot.com