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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 5B1E3C43387 for ; Wed, 16 Jan 2019 10:25:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2AAD820840 for ; Wed, 16 Jan 2019 10:25:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389093AbfAPKZC (ORCPT ); Wed, 16 Jan 2019 05:25:02 -0500 Received: from mail-qt1-f194.google.com ([209.85.160.194]:46236 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729269AbfAPKZB (ORCPT ); Wed, 16 Jan 2019 05:25:01 -0500 Received: by mail-qt1-f194.google.com with SMTP id y20so6480018qtm.13; Wed, 16 Jan 2019 02:25:00 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=LmsvamTKgo+58LgedZq1GakVrL3Oa2JR2r8mNl8nyVI=; b=at40uF9gLXB73WLeylDk4mWsjDDoWC4/NInB81kafbFudIfBExFllmxGU76u1t3xP+ HZR176KSEqAPGffLgp26/tI/taeOUEOY150tgjQnY3/KqzCxvlZxqz5WvhNP6T5LvF4M DEk8tnmB4QGeQGx4joSgqXw/AAduKD8gzpFCAJjCCCJ0m9uw2ZYta3zFNjGWJabtOeTH g6+A0jtC/6e9aM++0aK95MdK3C2Uk/wMxwCSeCXAZaKin9GQH0siNPVl2s4Lwx8a9xZD zmOAMFIWf1qKmwOT5Oh3kUjmbpPGJ2Hn7ANGzrvIrewur24h3cjQFgh6qyHeggkfveLs /Ljg== X-Gm-Message-State: AJcUukexUsqLrtTJ9YALKLDVEPcXs9zGzRyqNMSREjV0rAkhmio0mMde jShGj4eoBnToYcRLpW40WfEP/XGtTIFWyJqxrVk= X-Google-Smtp-Source: ALg8bN7TPbSuZQ+urcPiZwntG9alwIAaqb+En/OZwB7UWwOChTvYfu39fhAsU8v0s7alyqMW/8JP2hpa18mO9YsbWWc= X-Received: by 2002:ac8:1d12:: with SMTP id d18mr6344298qtl.343.1547634300459; Wed, 16 Jan 2019 02:25:00 -0800 (PST) MIME-Version: 1.0 References: <20190114095804.27978-1-hch@lst.de> In-Reply-To: From: Arnd Bergmann Date: Wed, 16 Jan 2019 11:24:43 +0100 Message-ID: Subject: Re: remove block layer bounce buffering for MMC To: Ulf Hansson Cc: Christoph Hellwig , Linus Walleij , Russell King , Nicolas Pitre , Aaro Koskinen , Ben Dooks , "linux-mmc@vger.kernel.org" , Linux ARM , linux-omap , "list@263.net:IOMMU DRIVERS , Joerg Roedel ," , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 14, 2019 at 11:27 AM Ulf Hansson wrote: > > +Linus Walleij (recently made a cleanup of the mmc bounce buffering code). > > On Mon, 14 Jan 2019 at 10:58, Christoph Hellwig wrote: > > > > Hi everyone, > > > > this series converts the remaining MMC host drivers to properly kmap the > > scatterlist entries it does PIO operations on, and then goes on to > > remove the usage of block layer bounce buffering (which I plan to remove > > eventually) from the MMC layer. > > > > As a bonus I've converted various drivers to the proper scatterlist > > helpers so that at least in theory they are ready for chained > > scatterlists. > > > > All the changes are compile tested only as I don't have any of the > > hardware, so a careful review would be appreciated. > > Thanks for posting this. I will have a look as soon as I can, but > first needs to catch up with things since the holidays. Linus probably knows more here, but I have a vague recollection of the MMC bounce buffer code being needed mostly for performance reasons: when the scatterlist is discontiguous, that can result in a request being split up into separate MMC commands, which due to the lack of queued commands combined with the need for garbage collection on sub-page writes results in a huge slowdown compared to having larger bounce buffers all the time. We had discussed finding a different way to do this (separate from the bounce buffering), but I don't know if that ever happened, or if this is even the code that you are changing here. Arnd