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=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 77A06C433DF for ; Thu, 16 Jul 2020 10:24:13 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 438F1204EA for ; Thu, 16 Jul 2020 10:24:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="iqMjVMkp"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="O7qT433B" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 438F1204EA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Zf6YhFO05pktvSkZaNatVoxnycaF7MLoX7QbsPcMsms=; b=iqMjVMkpG5zRBO2J9YGWfcmsF edvGVtdwHyy+emsxuTvfqu0lug4uv1nYtpb0b2vIjaE69XzxUHyyLT6W3LWR2oRKCudk0Y7uUheeC vwVaoAqxsTuGR0PBk1BzMLT5+HDxVvE9Ao3tPOYa1FbT6aycML3BVZVgHNVhHNu2f672SZTT6xUtt ublCfG0F1TWtezg4KP7VIy9PuEBlPT45D/F3haFWDZiabKvwiZuB5GJlrdhRC/+CvM6LIEQ+vfGrC U6BrY058deA6uKB38M9YpI8oJozLMF+q7uSBksfLj2kIcSkMCxMn1PogRjBVXDmxzSA+i00UAXhHp VN3XBOFbw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jw12G-0004Mr-Gz; Thu, 16 Jul 2020 10:22:40 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jw12E-0004MC-Lv for linux-arm-kernel@lists.infradead.org; Thu, 16 Jul 2020 10:22:39 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 89A51204EA; Thu, 16 Jul 2020 10:22:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594894958; bh=vzEaE1HWTa7LYtbebB7ritpzkpel2YtikBtG3CEZDzU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=O7qT433Bf508kbmPUyZtGJ1ha3eKm5yrmKHurnYxiVO1tk+RfIFdFzfIP9a4dEULJ cxskKb6f2hESv3IlEBT1RUtZQsbEm8i3bC2eetulC0gX+ABbte+A6hbUMZv5oMxo3Z dEeF7i7CvTyJM+Yn2p8YoEk1EHckrb6iEUSt+mB4= Date: Thu, 16 Jul 2020 11:22:33 +0100 From: Will Deacon To: John Garry Subject: Re: [PATCH 0/4] iommu/arm-smmu-v3: Improve cmdq lock efficiency Message-ID: <20200716102233.GC7036@willie-the-truck> References: <1592846920-45338-1-git-send-email-john.garry@huawei.com> <20200716101940.GA7036@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200716101940.GA7036@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200716_062238_798661_4D2AE4C6 X-CRM114-Status: GOOD ( 12.58 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: trivial@kernel.org, maz@kernel.org, joro@8bytes.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, iommu@lists.linux-foundation.org, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Jul 16, 2020 at 11:19:41AM +0100, Will Deacon wrote: > On Tue, Jun 23, 2020 at 01:28:36AM +0800, John Garry wrote: > > As mentioned in [0], the CPU may consume many cycles processing > > arm_smmu_cmdq_issue_cmdlist(). One issue we find is the cmpxchg() loop to > > get space on the queue takes approx 25% of the cycles for this function. > > > > This series removes that cmpxchg(). > > How about something much simpler like the diff below? Ah, scratch that, I don't drop the lock if we fail the cas with it held. Let me hack it some more (I have no hardware so I can only build-test this). Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel