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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6541C43334 for ; Wed, 8 Jun 2022 17:39:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232525AbiFHRjW (ORCPT ); Wed, 8 Jun 2022 13:39:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40386 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232517AbiFHRjR (ORCPT ); Wed, 8 Jun 2022 13:39:17 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 43D942AD1; Wed, 8 Jun 2022 10:39:15 -0700 (PDT) Received: from fraeml734-chm.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4LJDqk4F4Cz6884T; Thu, 9 Jun 2022 01:34:26 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml734-chm.china.huawei.com (10.206.15.215) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 8 Jun 2022 19:39:12 +0200 Received: from [10.47.90.54] (10.47.90.54) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 8 Jun 2022 18:39:11 +0100 Message-ID: Date: Wed, 8 Jun 2022 18:39:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH v3 2/4] dma-iommu: Add iommu_dma_opt_mapping_size() To: Bart Van Assche , , , , , , , , CC: , , , , , References: <1654507822-168026-1-git-send-email-john.garry@huawei.com> <1654507822-168026-3-git-send-email-john.garry@huawei.com> From: John Garry In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.47.90.54] X-ClientProxiedBy: lhreml744-chm.china.huawei.com (10.201.108.194) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-ide@vger.kernel.org On 08/06/2022 18:26, Bart Van Assche wrote: > On 6/6/22 02:30, John Garry via iommu wrote: >> +unsigned long iova_rcache_range(void) >> +{ >> +    return PAGE_SIZE << (IOVA_RANGE_CACHE_MAX_SIZE - 1); >> +} > > My understanding is that iova cache entries may be smaller than > IOVA_RANGE_CACHE_MAX_SIZE and hence that even if code that uses the DMA > mapping API respects this limit that a cache miss can still happen. Sure, a cache miss may still happen - however once we have stressed the system for a while then the rcaches fill up and don't fail often, or often enough to be noticeable compared to not having a cached IOVAs at all. Thanks, john