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=DKIM_INVALID,DKIM_SIGNED, 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 3FE82C7618B for ; Wed, 24 Jul 2019 14:07:59 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 12DA022ADA for ; Wed, 24 Jul 2019 14:07:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="taPCRfGP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 12DA022ADA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id DF53EE3E; Wed, 24 Jul 2019 14:07:58 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id D85E4E2F for ; Wed, 24 Jul 2019 14:07:57 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 90CE8FE for ; Wed, 24 Jul 2019 14:07:57 +0000 (UTC) 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 3686A21BF6; Wed, 24 Jul 2019 14:07:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563977277; bh=q5JArXbSQPR5xLurBAUTeK3QW8R25A1YF+BwHv3RCv4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=taPCRfGPAORqO7RV/BtaQZ8r/flUjO9VftImmFiZPtnvhdmKZpsplTPs5fWdZrRlM xux6EPmXj+2UrewDPGaOx7I4BPmspz7eqDxMeVgw0MpW+SU5PSq00Zet6Jn4fqzblA ToZgIA8OhbmKtM7Qh9DUbpXWTEHiliBAG4pa5vw0= Date: Wed, 24 Jul 2019 15:07:52 +0100 From: Will Deacon To: John Garry Subject: Re: [RFC PATCH v2 18/19] iommu/arm-smmu-v3: Reduce contention during command-queue insertion Message-ID: <20190724140751.pewgh4v5bmlmub23@willie-the-truck> References: <20190711171927.28803-1-will@kernel.org> <20190711171927.28803-19-will@kernel.org> <8a1be404-f22a-1f96-2f0d-4cf35ca99d2d@huawei.com> <20190724121548.j5tekad45kwlobvs@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Cc: Vijay Kilary , Jean-Philippe Brucker , Jon Masters , Jan Glauber , Alex Williamson , iommu@lists.linux-foundation.org, Jayachandran Chandrasekharan Nair , Robin Murphy X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On Wed, Jul 24, 2019 at 03:03:20PM +0100, John Garry wrote: > On 24/07/2019 13:15, Will Deacon wrote: > > > Could it be a minor optimisation to advance the HW producer pointer at this > > > stage for the owner only? We know that its entries are written, and it > > > should be first in the new batch of commands (right?), so we could advance > > > the pointer to at least get the HW started. > > > > I think that would be a valid thing to do, but it depends on the relative > > cost of writing to prod compared to how long we're likely to wait. Given > > that everybody has irqs disabled when writing out their commands, I wouldn't > > expect the waiting to be a big issue, > > For sure, but I'm thinking of the possible scenario where the the guy(s) > we're waiting on have many more commands. Or they just joined the current > gathering quite late, just prior to clearing the owner flag. Understood, but a "cacheable" memcpy (assuming the SMMU is coherent) should be pretty quick, even for maximum batch size I think. > although we could probably optimise > > arm_smmu_cmdq_write_entries() into a memcpy() if we needed to. > > > > In other words, I think we need numbers to justify that change. > > Anyway, this is quite minor, and I will see if the change could be justified > by numbers. Thanks! If the numbers show it's useful, we can definitely add it. Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu