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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 0A8ADC06513 for ; Thu, 4 Jul 2019 12:04:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CBBBE21850 for ; Thu, 4 Jul 2019 12:04:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="reCYBa/H" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727684AbfGDMEs (ORCPT ); Thu, 4 Jul 2019 08:04:48 -0400 Received: from mail-wm1-f68.google.com ([209.85.128.68]:38267 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727600AbfGDMEs (ORCPT ); Thu, 4 Jul 2019 08:04:48 -0400 Received: by mail-wm1-f68.google.com with SMTP id s15so5893569wmj.3 for ; Thu, 04 Jul 2019 05:04:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=amr/MLN9cI5Ec8HWgSABL9rUXzQlcR+yO98qbl8sqQQ=; b=reCYBa/HDiyEd6CU/NQNeECZ0TGiSTj8f8SEw4WFvGQo59bH5871qj/oJ9PYzgM4GP zA95ZBUcbKacoYmCK12EVNylEKYfkwbrorMv9FA5F0SvbjQHxdo8QpW1OmqvBTDGYNak zkF4lXTMeJnHNJRfmUlhCwG7yFK7GzrKEx2gRXlMS6sgu712/cFTieIviLBBe/2wP+x6 oBfEeXDD9MTQs5r9JnNseOOa9Q4u0PoebNFFoi4vfhDYpljevyDegYuh1dD1kWAYAmsL 8tQjrV6Klmf/TwqngR513k5F/mMIIr1dUgGU4aw0KWGD5w7OQcLph+aEc3Tt0DgWYslh mZ0w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=amr/MLN9cI5Ec8HWgSABL9rUXzQlcR+yO98qbl8sqQQ=; b=b5T+xP3boEtEtxxAT7zRN+0g1PnB+pYnW9z/Xy88aFU5fiJ51vfz7bdVjfM//eDjp1 tPfNKB0KCvrPKvqZ7RV0ZoFWtwdSQNO3Bi57LcCxLC6ukRXQU6SqUaskirm90wWrQbt0 gT+a7LjgweoE/KGvU2B8QBKSaDhgHDUd/TUKOYtw/wG1/iJmqzuf3rY2Sqil/ULvYRsK XKjVRojDHi6IsZGXFcy1YHh+iPj0D/tGJBe97+JBfPTmzWl++FTM++vWn9lpefAkBR7X OIPv+2yWi/OLYdXUx2rHQ31I18GG86BtEaFOwoi6+HmlapO/QXHFaPcH8IMnPOHiQdHZ yWLg== X-Gm-Message-State: APjAAAWxFvRefS7bQNQZiXiRtmADmOotxohaKw9LSkW+PRvA9Q8s0Hu9 R6+SBQ4v4HioKNCQmrcJFGouig== X-Google-Smtp-Source: APXvYqyT6y+9T+/VeJfNymSjJVbJMJkxGcTutUA49l/YNxwHZmt9KNlRem6wZWge7DDaiLLPkOPVCA== X-Received: by 2002:a7b:ce95:: with SMTP id q21mr12611948wmj.65.1562241885365; Thu, 04 Jul 2019 05:04:45 -0700 (PDT) Received: from apalos (athedsl-428434.home.otenet.gr. [79.131.225.144]) by smtp.gmail.com with ESMTPSA id z9sm7475960wrs.14.2019.07.04.05.04.43 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 04 Jul 2019 05:04:44 -0700 (PDT) Date: Thu, 4 Jul 2019 15:04:41 +0300 From: Ilias Apalodimas To: Jesper Dangaard Brouer Cc: Jose Abreu , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-stm32@st-md-mailman.stormreply.com" , "linux-arm-kernel@lists.infradead.org" , Joao Pinto , "David S . Miller" , Giuseppe Cavallaro , Alexandre Torgue , Maxime Coquelin , Maxime Ripard , Chen-Yu Tsai Subject: Re: [PATCH net-next 3/3] net: stmmac: Introducing support for Page Pool Message-ID: <20190704120441.GA6866@apalos> References: <1b254bb7fc6044c5e6e2fdd9e00088d1d13a808b.1562149883.git.joabreu@synopsys.com> <20190704120018.4523a119@carbon> <20190704135414.0dd5df76@carbon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190704135414.0dd5df76@carbon> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jesper, > On Thu, 4 Jul 2019 10:13:37 +0000 > Jose Abreu wrote: > > > The page_pool DMA mapping cannot be "kept" when page traveling into the > > > network stack attached to an SKB. (Ilias and I have a long term plan[1] > > > to allow this, but you cannot do it ATM). > > > > The reason I recycle the page is this previous call to: > > > > skb_copy_to_linear_data() > > > > So, technically, I'm syncing to CPU the page(s) and then memcpy to a > > previously allocated SKB ... So it's safe to just recycle the mapping I > > think. > > I didn't notice the skb_copy_to_linear_data(), will copy the entire > frame, thus leaving the page unused and avail for recycle. Yea this is essentially a 'copybreak' without the byte limitation that other drivers usually impose (remember mvneta was doing this for all packets < 256b) That's why i was concerned on what will happen on > 1000b frames and what the memory pressure is going to be. The trade off here is copying vs mapping/unmapping. > > Then it looks like you are doing the correct thing. I will appreciate > if you could add a comment above the call like: > > /* Data payload copied into SKB, page ready for recycle */ > page_pool_recycle_direct(rx_q->page_pool, buf->page); > > > > Its kind of using bounce buffers and I do see performance gain in this > > (I think the reason is because my setup uses swiotlb for DMA mapping). > > > > Anyway, I'm open to some suggestions on how to improve this ... > > I was surprised to see page_pool being used outside the surrounding XDP > APIs (included/net/xdp.h). For you use-case, where you "just" use > page_pool as a driver-local fast recycle-allocator for RX-ring that > keeps pages DMA mapped, it does make a lot of sense. It simplifies the > driver a fair amount: > > 3 files changed, 63 insertions(+), 144 deletions(-) > > Thanks for demonstrating a use-case for page_pool besides XDP, and for > simplifying a driver with this. Same here thanks Jose, > > > > > Also remember that the page_pool requires you driver to do the > > > DMA-sync operation. I see a dma_sync_single_for_cpu(), but I > > > didn't see a dma_sync_single_for_device() (well, I noticed one > > > getting removed). (For some HW Ilias tells me that the > > > dma_sync_single_for_device can be elided, so maybe this can still > > > be correct for you). > > > > My HW just needs descriptors refilled which are in different coherent > > region so I don't see any reason for dma_sync_single_for_device() ... > > For you use-case, given you are copying out the data, and not writing > into it, then I don't think you need to do sync for device (before > giving the device the page again for another RX-ring cycle). > > The way I understand the danger: if writing to the DMA memory region, > and not doing the DMA-sync for-device, then the HW/coherency-system can > write-back the memory later. Which creates a race with the DMA-device, > if it is receiving a packet and is doing a write into same DMA memory > region. Someone correct me if I misunderstood this... Similar understanding here Cheers /Ilias