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=-2.3 required=3.0 tests=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 DF836C3A59E for ; Sat, 24 Aug 2019 05:15:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B600320870 for ; Sat, 24 Aug 2019 05:15:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726068AbfHXFPq (ORCPT ); Sat, 24 Aug 2019 01:15:46 -0400 Received: from mga11.intel.com ([192.55.52.93]:24229 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725777AbfHXFPq (ORCPT ); Sat, 24 Aug 2019 01:15:46 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Aug 2019 22:15:45 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,424,1559545200"; d="scan'208";a="196627309" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.147.113]) by fmsmga001.fm.intel.com with ESMTP; 23 Aug 2019 22:15:43 -0700 Date: Sat, 24 Aug 2019 13:16:05 +0800 From: Feng Tang To: Thomas Zimmermann Cc: Stephen Rothwell , Rong Chen , michel@daenzer.net, linux-kernel@vger.kernel.org, dri-devel , ying.huang@intel.com, lkp@01.org Subject: Re: [LKP] [drm/mgag200] 90f479ae51: vm-scalability.median -18.8% regression Message-ID: <20190824051605.GA63850@shbuild999.sh.intel.com> References: <14fdaaed-51c8-b270-b46b-cba7b5c4ba52@suse.de> <20190805070200.GA91650@shbuild999.sh.intel.com> <045a23ab-78f7-f363-4a2e-bf24a7a2f79e@suse.de> <37ae41e4-455d-c18d-5c93-7df854abfef9@intel.com> <370747ca-4dc9-917b-096c-891dcc2aedf0@suse.de> <20190812072545.GA63191@shbuild999.sh.intel.com> <20190813093616.GA65475@shbuild999.sh.intel.com> <64d41701-55a4-e526-17ae-8936de4bc1ef@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <64d41701-55a4-e526-17ae-8936de4bc1ef@suse.de> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Thomas, On Thu, Aug 22, 2019 at 07:25:11PM +0200, Thomas Zimmermann wrote: > Hi > > I was traveling and could reply earlier. Sorry for taking so long. No problem! I guessed so :) > > Am 13.08.19 um 11:36 schrieb Feng Tang: > > Hi Thomas, > > > > On Mon, Aug 12, 2019 at 03:25:45PM +0800, Feng Tang wrote: > >> Hi Thomas, > >> > >> On Fri, Aug 09, 2019 at 04:12:29PM +0800, Rong Chen wrote: > >>> Hi, > >>> > >>>>> Actually we run the benchmark as a background process, do we need to > >>>>> disable the cursor and test again? > >>>> There's a worker thread that updates the display from the shadow buffer. > >>>> The blinking cursor periodically triggers the worker thread, but the > >>>> actual update is just the size of one character. > >>>> > >>>> The point of the test without output is to see if the regression comes > >>> >from the buffer update (i.e., the memcpy from shadow buffer to VRAM), or > >>> >from the worker thread. If the regression goes away after disabling the > >>>> blinking cursor, then the worker thread is the problem. If it already > >>>> goes away if there's simply no output from the test, the screen update > >>>> is the problem. On my machine I have to disable the blinking cursor, so > >>>> I think the worker causes the performance drop. > >>> > >>> We disabled redirecting stdout/stderr to /dev/kmsg,  and the regression is > >>> gone. > >>> > >>> commit: > >>>   f1f8555dfb9 drm/bochs: Use shadow buffer for bochs framebuffer console > >>>   90f479ae51a drm/mgag200: Replace struct mga_fbdev with generic framebuffer > >>> emulation > >>> > >>> f1f8555dfb9a70a2  90f479ae51afa45efab97afdde testcase/testparams/testbox > >>> ----------------  -------------------------- --------------------------- > >>>          %stddev      change         %stddev > >>>              \          |                \ > >>>      43785                       44481 > >>> vm-scalability/300s-8T-anon-cow-seq-hugetlb/lkp-knm01 > >>>      43785                       44481        GEO-MEAN vm-scalability.median > >> > >> Till now, from Rong's tests: > >> 1. Disabling cursor blinking doesn't cure the regression. > >> 2. Disabling printint test results to console can workaround the > >> regression. > >> > >> Also if we set the perfer_shadown to 0, the regression is also > >> gone. > > > > We also did some further break down for the time consumed by the > > new code. > > > > The drm_fb_helper_dirty_work() calls sequentially > > 1. drm_client_buffer_vmap (290 us) > > 2. drm_fb_helper_dirty_blit_real (19240 us) > > 3. helper->fb->funcs->dirty() ---> NULL for mgag200 driver > > 4. drm_client_buffer_vunmap (215 us) > > > > It's somewhat different to what I observed, but maybe I just couldn't > reproduce the problem correctly. > > > The average run time is listed after the function names. > > > > From it, we can see drm_fb_helper_dirty_blit_real() takes too long > > time (about 20ms for each run). I guess this is the root cause > > of this regression, as the original code doesn't use this dirty worker. > > True, the original code uses a temporary buffer, but updates the display > immediately. > > My guess is that this could be a caching problem. The worker runs on a > different CPU, which doesn't have the shadow buffer in cache. Yes, that's my thought too. I profiled the working set size, for most of the drm_fb_helper_dirty_blit_real(), it will update a buffer 4096x768(3 MB), and as it is called 30~40 times per second, it surely will affect the cache. > > As said in last email, setting the prefer_shadow to 0 can avoid > > the regrssion. Could it be an option? > > Unfortunately not. Without the shadow buffer, the console's display > buffer permanently resides in video memory. It consumes significant > amount of that memory (say 8 MiB out of 16 MiB). That doesn't leave > enough room for anything else. > > The best option is to not print to the console. Do we have other options here? My thought is this is clearly a regression, that the old driver works fine, while the new version in linux-next doesn't. Also for a frame buffer console, writting dozens line of message to it is not a rare user case. We have many test platforms (servers/desktops/laptops) with different kinds of GFX hardwares, and this model works fine for many years :) Thanks, Feng > Best regards > Thomas > > > Thanks, > > Feng > > > >> > >> --- a/drivers/gpu/drm/mgag200/mgag200_main.c > >> +++ b/drivers/gpu/drm/mgag200/mgag200_main.c > >> @@ -167,7 +167,7 @@ int mgag200_driver_load(struct drm_device *dev, unsigned long flags) > >> dev->mode_config.preferred_depth = 16; > >> else > >> dev->mode_config.preferred_depth = 32; > >> - dev->mode_config.prefer_shadow = 1; > >> + dev->mode_config.prefer_shadow = 0; > >> > >> And from the perf data, one obvious difference is good case don't > >> call drm_fb_helper_dirty_work(), while bad case calls. > >> > >> Thanks, > >> Feng > >> > >>> Best Regards, > >>> Rong Chen > > _______________________________________________ > > dri-devel mailing list > > dri-devel@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > -- > Thomas Zimmermann > Graphics Driver Developer > SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany > GF: Felix Imendörffer, Mary Higgins, Sri Rasiah > HRB 21284 (AG Nürnberg) >