Return-Path: Received: from mx143.netapp.com ([216.240.21.24]:19807 "EHLO mx143.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754963AbbIHPHY (ORCPT ); Tue, 8 Sep 2015 11:07:24 -0400 Subject: Re: [PATCH v1 0/8] VFS: In-kernel copy system call To: Andreas Dilger References: <1441397823-1203-1-git-send-email-Anna.Schumaker@Netapp.com> <4B41043F-5D85-42D6-8F20-2DCC45930EF4@dilger.ca> CC: , , , , , , , , , , From: Anna Schumaker Message-ID: <55EEF9A7.8090600@Netapp.com> Date: Tue, 8 Sep 2015 11:07:19 -0400 MIME-Version: 1.0 In-Reply-To: <4B41043F-5D85-42D6-8F20-2DCC45930EF4@dilger.ca> Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: On 09/04/2015 06:25 PM, Andreas Dilger wrote: > On Sep 4, 2015, at 2:16 PM, Anna Schumaker wrote: >> >> Copy system calls came up during Plumbers a couple of weeks ago, >> because several filesystems (including NFS and XFS) are currently >> working on copy acceleration implementations. We haven't heard from >> Zach Brown in a while, so I volunteered to push his patches upstream >> so individual filesystems don't need to keep writing their own ioctls. >> >> The first three patches are a simple reposting of Zach's patches >> from several months ago, with one minor error code fix. The remaining >> patches add in a fallback mechanism when filesystems don't provide a >> copy function. This is especially useful when doing a server-side >> copy on NFS (using the new COPY operation in NFS v4.2). This fallback >> can be disabled by passing the flag COPY_REFLINK to the system call. >> >> The last patch is a man page patch documenting this new system call, >> including an example program. >> >> I tested the fallback option by using /dev/urandom to generate files >> of varying sizes and copying them. I compared the time to copy >> against that of `cp` just to see if there is a noticable difference. >> I found that runtimes are roughly the same, but in-kernel copy tends >> to use less of the cpu. Values in the tables below are averages >> across multiple trials. >> >> >> /usr/bin/cp | 512 MB | 1024 MB | 1536 MB | 2048 MB >> -------------|-----------|-----------|-----------|----------- >> user | 0.00s | 0.00s | 0.00s | 0.00s >> system | 0.32s | 0.52s | 1.04s | 1.04s >> cpu | 73% | 69% | 62% | 62% >> total | 0.446 | 0.757 | 1.197 | 1.667 >> >> >> VFS copy | 512 MB | 1024 MB | 1536 MB | 2048 MB >> -------------|-----------|-----------|-----------|----------- >> user | 0.00s | 0.00s | 0.00s | 0.00s >> system | 0.33s | 0.49s | 0.76s | 0.99s >> cpu | 77% | 62% | 60% | 59% >> total | 0.422 | 0.777 | 1.267 | 1.655 >> >> >> Questions? Comments? Thoughts? > > 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? I tested using XFS against two KVM guests. Maybe something there is adding the extra cpu cycles? Anna > > In theory, the VFS copy routines should save at least 50% of the > CPU usage since it only needs to make one copy (src->dest) instead > of two (kernel->user, user->kernel). Ideally it wouldn't make any > data copies at all and just pass page references from the source > to the target. > > Cheers, Andreas >> >> Anna >> >> >> Anna Schumaker (5): >> btrfs: Add mountpoint checking during btrfs_copy_file_range >> vfs: Remove copy_file_range mountpoint checks >> vfs: Copy should check len after file open mode >> vfs: Copy should use file_out rather than file_in >> vfs: Fall back on splice if no copy function defined >> >> Zach Brown (3): >> vfs: add copy_file_range syscall and vfs helper >> x86: add sys_copy_file_range to syscall tables >> btrfs: add .copy_file_range file operation >> >> arch/x86/entry/syscalls/syscall_32.tbl | 1 + >> arch/x86/entry/syscalls/syscall_64.tbl | 1 + >> fs/btrfs/ctree.h | 3 + >> fs/btrfs/file.c | 1 + >> fs/btrfs/ioctl.c | 95 ++++++++++++++---------- >> fs/read_write.c | 132 +++++++++++++++++++++++++++++++++ >> include/linux/copy.h | 6 ++ >> include/linux/fs.h | 3 + >> include/uapi/asm-generic/unistd.h | 4 +- >> include/uapi/linux/Kbuild | 1 + >> include/uapi/linux/copy.h | 6 ++ >> kernel/sys_ni.c | 1 + >> 12 files changed, 214 insertions(+), 40 deletions(-) >> create mode 100644 include/linux/copy.h >> create mode 100644 include/uapi/linux/copy.h >> >> -- >> 2.5.1 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > Cheers, Andreas > > > > >