Return-Path: Received: from mail-qk0-f180.google.com ([209.85.220.180]:33298 "EHLO mail-qk0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751078AbdFAM7Y (ORCPT ); Thu, 1 Jun 2017 08:59:24 -0400 Received: by mail-qk0-f180.google.com with SMTP id y201so35311386qka.0 for ; Thu, 01 Jun 2017 05:59:24 -0700 (PDT) Message-ID: <1496321961.2845.6.camel@redhat.com> Subject: Re: [lkp-robot] [fs/locks] 9d21d181d0: will-it-scale.per_process_ops -14.1% regression From: Jeff Layton To: Benjamin Coddington Cc: kernel test robot , Alexander Viro , bfields@fieldses.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, lkp@01.org, Christoph Hellwig Date: Thu, 01 Jun 2017 08:59:21 -0400 In-Reply-To: <8F2C3CFF-5C2D-41B0-A895-B1F074DA7943@redhat.com> References: <20170601020556.GE16905@yexl-desktop> <1496317284.2845.4.camel@redhat.com> <8F2C3CFF-5C2D-41B0-A895-B1F074DA7943@redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, 2017-06-01 at 07:49 -0400, Benjamin Coddington wrote: > On 1 Jun 2017, at 7:41, Jeff Layton wrote: > > > On Thu, 2017-06-01 at 10:05 +0800, kernel test robot wrote: > > > Greeting, > > > > > > FYI, we noticed a -14.1% regression of will-it-scale.per_process_ops > > > due to commit: > > > > > > > > > commit: 9d21d181d06acab9a8e80eac2ec4eed77b656793 ("fs/locks: Set > > > fl_nspid at file_lock allocation") > > > url: > > > https://github.com/0day-ci/linux/commits/Benjamin-Coddington/fs-locks-Alloc-file_lock-where-practical/20170527-050700 > > > > > > > > > > Ouch, that's a rather nasty performance hit. In hindsight, maybe we > > shouldn't move those off the stack after all? Heck, if it's that > > significant, maybe we should move the F_SETLK callers to allocate > > these > > on the stack as well? > > We can do that. But, I think this is picking up the > locks_mandatory_area() > allocation which is now removed. The attached config has > CONFIG_MANDATORY_FILE_LOCKING=y, so there's allocation on every > read/write. > I'm not so sure. That would only be the case if the thing were marked for manadatory locking (a really rare thing). The test is really simple and I don't think any read/write activity is involved: https://github.com/antonblanchard/will-it-scale/blob/master/tests/lock1.c ...and the 0 day bisected it down to this patch, IIUC: https://github.com/0day-ci/linux/commit/9d21d181d06acab9a8e80eac2ec4eed77b656793 It seems likely that it's the extra get_pid/put_pid in the allocation and free codepath. I expected those to be pretty cheap, but maybe they're not? -- Jeff Layton