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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 9B874C433DF for ; Fri, 14 Aug 2020 20:18:25 +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 30F6420768 for ; Fri, 14 Aug 2020 20:18:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 30F6420768 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 CD2B16EC15; Fri, 14 Aug 2020 20:18:24 +0000 (UTC) Received: from fireflyinternet.com (unknown [77.68.26.236]) by gabe.freedesktop.org (Postfix) with ESMTPS id 453726EC15 for ; Fri, 14 Aug 2020 20:18:23 +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 22131781-1500050 for multiple; Fri, 14 Aug 2020 21:18:21 +0100 MIME-Version: 1.0 In-Reply-To: <159743409290.31882.4297809836771338545@build.alporthouse.com> References: <20200814155735.29138-1-chris@chris-wilson.co.uk> <20200814155735.29138-3-chris@chris-wilson.co.uk> <87ft8p135h.fsf@gaia.fi.intel.com> <159743409290.31882.4297809836771338545@build.alporthouse.com> From: Chris Wilson To: Mika Kuoppala , intel-gfx@lists.freedesktop.org Date: Fri, 14 Aug 2020 21:18:19 +0100 Message-ID: <159743629912.31882.4041606652398941372@build.alporthouse.com> User-Agent: alot/0.9 Subject: Re: [Intel-gfx] [PATCH 3/3] drm/i915/gt: Apply the CSB w/a for all 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Quoting Chris Wilson (2020-08-14 20:41:32) > Quoting Mika Kuoppala (2020-08-14 19:41:14) > > Chris Wilson writes: > > > - entry = READ_ONCE(*csb); > > > - if (unlikely(entry == -1)) { > > > - preempt_disable(); > > > - if (wait_for_atomic_us((entry = READ_ONCE(*csb)) != -1, 50)) > > > > If we get this deep into desperation, should we start to apply more > > pressure. Ie, rmb instead of just instructing the compiler. And could also > > start to invalidate the entry which obviously if of no use. > > I had a rmb() here; removing it did not appear to make any difference > whatsoever to the average delay. The extreme case would be a full > mb(); clflush(); mb() read. I haven't timed the average for that.... +static inline u64 __csb_read(u64 *csb) +{ + mb(); + clflush(csb); + mb(); + + return READ_ONCE(*csb); +} [ 1554.274204] csb: 1793 misses, avg 475ns, max 14727ns So no better on average or at worst. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx