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 4F7C8C0015E for ; Fri, 28 Jul 2023 12:39:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236592AbjG1Mjc (ORCPT ); Fri, 28 Jul 2023 08:39:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52024 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233367AbjG1Mj2 (ORCPT ); Fri, 28 Jul 2023 08:39:28 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7F8EB187; Fri, 28 Jul 2023 05:39:27 -0700 (PDT) Received: from dggpemm500005.china.huawei.com (unknown [172.30.72.57]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4RC6Zl4YsJzLnt2; Fri, 28 Jul 2023 20:36:47 +0800 (CST) Received: from [10.69.30.204] (10.69.30.204) by dggpemm500005.china.huawei.com (7.185.36.74) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Fri, 28 Jul 2023 20:39:24 +0800 Subject: Re: [PATCH net-next 6/9] page_pool: avoid calling no-op externals when possible To: Alexander Lobakin , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni CC: Maciej Fijalkowski , Larysa Zaremba , Alexander Duyck , Jesper Dangaard Brouer , Ilias Apalodimas , Simon Horman , , References: <20230727144336.1646454-1-aleksander.lobakin@intel.com> <20230727144336.1646454-7-aleksander.lobakin@intel.com> From: Yunsheng Lin Message-ID: Date: Fri, 28 Jul 2023 20:39:24 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20230727144336.1646454-7-aleksander.lobakin@intel.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.69.30.204] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500005.china.huawei.com (7.185.36.74) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/7/27 22:43, Alexander Lobakin wrote: > Turned out page_pool_put{,_full}_page() can burn quite a bunch of cycles > even when on DMA-coherent platforms (like x86) with no active IOMMU or > swiotlb, just for the call ladder. > Indeed, it's > > page_pool_put_page() > page_pool_put_defragged_page() <- external > __page_pool_put_page() > page_pool_dma_sync_for_device() <- non-inline > dma_sync_single_range_for_device() > dma_sync_single_for_device() <- external > dma_direct_sync_single_for_device() > dev_is_dma_coherent() <- exit > > For the inline functions, no guarantees the compiler won't uninline them > (they're clearly not one-liners and sometimes compilers uninline even > 2 + 2). The first external call is necessary, but the rest 2+ are done > for nothing each time, plus a bunch of checks here and there. > Since Page Pool mappings are long-term and for one "device + addr" pair > dma_need_sync() will always return the same value (basically, whether it > belongs to an swiotlb pool), addresses can be tested once right after > they're obtained and the result can be reused until the page is unmapped. > Define the new PP DMA sync operation type, which will mean "do DMA syncs > for the device, but only when needed" and turn it on by default when the > driver asks to sync pages. When a page is mapped, check whether it needs > syncs and if so, replace that "sync when needed" back to "always do > syncs" globally for the whole pool (better safe than sorry). As long as > the pool has no pages requiring DMA syncs, this cuts off a good piece > of calls and checks. When at least one page required it, the pool > conservatively falls back to "always call sync functions", no per-page > verdicts. It's a fairly rare case anyway that only a few pages would > require syncing. > On my x86_64, this gives from 2% to 5% performance benefit with no > negative impact for cases when IOMMU is on and the shortcut can't be > used. > It seems other subsystem may have the similar problem as page_pool, is it possible to implement this kind of trick in the dma subsystem instead of every subsystem inventing their own trick?