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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 0AEA5C33CB1 for ; Thu, 16 Jan 2020 07:40:34 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DFAD92075B for ; Thu, 16 Jan 2020 07:40:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DFAD92075B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=chris-wilson.co.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9D1C76EC16; Thu, 16 Jan 2020 07:40:29 +0000 (UTC) Received: from fireflyinternet.com (mail.fireflyinternet.com [109.228.58.192]) by gabe.freedesktop.org (Postfix) with ESMTPS id A75606EC0D; Thu, 16 Jan 2020 07:40:27 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from localhost (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP (TLS) id 19896700-1500050 for multiple; Thu, 16 Jan 2020 07:40:22 +0000 MIME-Version: 1.0 To: Daniel Vetter From: Chris Wilson In-Reply-To: <20200116065242.GC8400@dvetter-linux.ger.corp.intel.com> References: <20200115205245.2772800-1-chris@chris-wilson.co.uk> <20200116065242.GC8400@dvetter-linux.ger.corp.intel.com> Message-ID: <157916041994.14122.8524532515240369595@skylake-alporthouse-com> User-Agent: alot/0.6 Date: Thu, 16 Jan 2020 07:40:19 +0000 Subject: Re: [Intel-gfx] [PATCH] drm: Inject a cond_resched() into long drm_clflush_sg() X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-gfx@lists.freedesktop.org, David Laight , dri-devel@lists.freedesktop.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Quoting Daniel Vetter (2020-01-16 06:52:42) > On Wed, Jan 15, 2020 at 08:52:45PM +0000, Chris Wilson wrote: > > Since we may try and flush the cachelines associated with large buffers > > (an 8K framebuffer is about 128MiB, even before we try HDR), this leads > > to unacceptably long latencies (when using a voluntary CONFIG_PREEMPT). > > If we call cond_resched() between each sg chunk, that it about every 128 > > pages, we have a natural break point in which to check if the process > > needs to be rescheduled. Naturally, this means that drm_clflush_sg() can > > only be called from process context -- which is true at the moment. The > > other clflush routines remain usable from atomic context. > > > > Even though flushing large objects takes a demonstrable amount to time > > to flush all the cachelines, clflush is still preferred over a > > system-wide wbinvd as the latter has unpredictable latencies affecting > > the whole system not just the local task. > > > > Reported-by: David Laight > > Signed-off-by: Chris Wilson > > Cc: David Laight > > The original bug report is complaining about latencies for SCHED_RT > threads, on a system that doesn't even use CONFIG_PREEMPT. I'm not sure > it's terribly valid to cater to that use-case - all the desktop distros > seem a lot more reasonable. So firmly *shrug* from my side ... Yeah, I had the same immediate response to the complaint), but otoh we've inserted cond_resched() before when it looks like may consume entire jiffies inside a loop. At the very minimum, we should have a might_sleep() here and a reminder that this can be very slow (remember byt?). -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx