Return-Path: Received: from zeniv.linux.org.uk ([195.92.253.2]:59116 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751206AbbIEIdr (ORCPT ); Sat, 5 Sep 2015 04:33:47 -0400 Date: Sat, 5 Sep 2015 09:33:42 +0100 From: Al Viro To: Andreas Dilger Cc: Anna Schumaker , linux-nfs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, zab@zabbo.net, clm@fb.com, darrick.wong@oracle.com, mtk.manpages@gmail.com, andros@netapp.com, hch@infradead.org Subject: Re: [PATCH v1 0/8] VFS: In-kernel copy system call Message-ID: <20150905083342.GG22011@ZenIV.linux.org.uk> References: <1441397823-1203-1-git-send-email-Anna.Schumaker@Netapp.com> <4B41043F-5D85-42D6-8F20-2DCC45930EF4@dilger.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <4B41043F-5D85-42D6-8F20-2DCC45930EF4@dilger.ca> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Sep 04, 2015 at 04:25:27PM -0600, Andreas Dilger wrote: > This is a bit of a surprising result, since in my testing in the > past, copy_{to/from}_user() is a major consumer of CPU time (50% > of a CPU core at 1GB/s). What backing filesystem did you test on? While we are at it, was cp(1) using read(2)/write(2) loop or was it using something else (sendfile(2), for example)?