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=-7.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 25E0AC433E6 for ; Wed, 20 Jan 2021 15:26:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC79F221FD for ; Wed, 20 Jan 2021 15:26:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403946AbhATP0n (ORCPT ); Wed, 20 Jan 2021 10:26:43 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:31607 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390864AbhATPNi (ORCPT ); Wed, 20 Jan 2021 10:13:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611155532; 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=m0WX/IW9qTI7pWygS2OV9t8yQ+iugqSZyKKAWy8i8Ng=; b=Q3Qr/1uFoCj2oZ+RSHr16kN0zvUkjivP6oK6ISezJiCaVM03csR7Mkk5R7R9E4nhvQjxCR VtJmuW5Kdg36JwaNYgQXdcz+pamYp13pA6Qy25fHC+POYIE+tPvdpExgMWRHP3s6xWtpNJ 0dRwynmVFYgi8rTV8b6H9zjFjhIkpTI= 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-212-i0lmVuOrNH2l7F-G-gW3wA-1; Wed, 20 Jan 2021 10:12:08 -0500 X-MC-Unique: i0lmVuOrNH2l7F-G-gW3wA-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 3DE2D8066E5; Wed, 20 Jan 2021 15:12:05 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 926EA608BA; Wed, 20 Jan 2021 15:12:04 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id 10KFC4DG027528; Wed, 20 Jan 2021 10:12:04 -0500 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id 10KFC1Sq027524; Wed, 20 Jan 2021 10:12:01 -0500 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Wed, 20 Jan 2021 10:12:01 -0500 (EST) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Jan Kara cc: Dave Chinner , Zhongwei Cai , "Theodore Ts'o" , Matthew Wilcox , David Laight , Mingkai Dong , Andrew Morton , Steven Whitehouse , Eric Sandeen , Dave Chinner , Wang Jianchao , Rajesh Tadakamadla , linux-kernel , linux-fsdevel , linux-nvdimm Subject: Re: Expense of read_iter In-Reply-To: <20210120141834.GA24063@quack2.suse.cz> Message-ID: References: <20210107151125.GB5270@casper.infradead.org> <17045315-CC1F-4165-B8E3-BA55DD16D46B@gmail.com> <2041983017.5681521.1610459100858.JavaMail.zimbra@sjtu.edu.cn> <1224425872.715547.1610703643424.JavaMail.zimbra@sjtu.edu.cn> <20210120044700.GA4626@dread.disaster.area> <20210120141834.GA24063@quack2.suse.cz> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 20 Jan 2021, Jan Kara wrote: > Yeah, I agree. I'm against ext4 private solution for this read problem. And > I'm also against duplicating ->read_iter functionatily in ->read handler. > The maintenance burden of this code duplication is IMHO just too big. We > rather need to improve the generic code so that the fast path is faster. > And every filesystem will benefit because this is not ext4 specific > problem. > > Honza Do you have some idea how to optimize the generic code that calls ->read_iter? vfs_read calls ->read if it is present. If not, it calls new_sync_read. new_sync_read's frame size is 128 bytes - it holds the structures iovec, kiocb and iov_iter. new_sync_read calls ->read_iter. I have found out that the cost of calling new_sync_read is 3.3%, Zhongwei found out 3.9%. (the benchmark repeatedy reads the same 4k page) I don't see any way how to optimize new_sync_read or how to reduce its frame size. Do you? Mikulas