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 705A4C77B78 for ; Wed, 26 Apr 2023 12:54:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240828AbjDZMyA (ORCPT ); Wed, 26 Apr 2023 08:54:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33852 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240523AbjDZMx6 (ORCPT ); Wed, 26 Apr 2023 08:53:58 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6EFB71720; Wed, 26 Apr 2023 05:53:56 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id EA54163665; Wed, 26 Apr 2023 12:53:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C0A4AC433D2; Wed, 26 Apr 2023 12:53:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1682513635; bh=rnR2gHMom5cZ9EE0QbaWG0mAQc/4BfAqxA6wiBHOddQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=0O5fefgIhXFVwx4bd/JHCnR2BWedmFunEuhy57jrlZSyAl3OzSBYYcehg0kqdST72 LDrHPOnCB314Vs0VFJJIEkS9b2AQwIuZKkVcvVjIisDaelGAgM9+dQ/hD/hIewmiWV KBROROmgExlXq2SJmL+iWP6rJn4hf+8RDIC0tFSM= Date: Wed, 26 Apr 2023 14:53:52 +0200 From: Greg Kroah-Hartman To: Petr =?utf-8?B?VGVzYcWZw61r?= Cc: Petr Tesarik , Jonathan Corbet , "Rafael J. Wysocki" , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , Christoph Hellwig , Marek Szyprowski , Robin Murphy , Borislav Petkov , "Paul E. McKenney" , Catalin Marinas , Will Deacon , Zhen Lei , Randy Dunlap , Damien Le Moal , Kim Phillips , "Steven Rostedt (Google)" , Muchun Song , Ondrej Zary , "Jason A. Donenfeld" , Petr Tesarik , Hans de Goede , Dan Williams , Andy Shevchenko , Kees Cook , Thomas Gleixner , Won Chung , "open list:DOCUMENTATION" , open list , "open list:DRM DRIVERS" , "open list:DMA MAPPING HELPERS" , Roberto Sassu , Kefeng Wang Subject: Re: [PATCH v2 0/7] Allow dynamic allocation of software IO TLB bounce buffers Message-ID: <2023042630-amends-speech-7db2@gregkh> References: <20230426141520.0caf4386@meshulam.tesarici.cz> <2023042617-wobble-enlighten-9361@gregkh> <20230426144439.5674f8bc@meshulam.tesarici.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230426144439.5674f8bc@meshulam.tesarici.cz> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 26, 2023 at 02:44:39PM +0200, Petr Tesařík wrote: > Hi Greg, > > On Wed, 26 Apr 2023 14:26:36 +0200 > Greg Kroah-Hartman wrote: > > > On Wed, Apr 26, 2023 at 02:15:20PM +0200, Petr Tesařík wrote: > > > Hi, > > > > > > On Wed, 19 Apr 2023 12:03:52 +0200 > > > Petr Tesarik wrote: > > > > > > > From: Petr Tesarik > > > > > > > > The goal of my work is to provide more flexibility in the sizing of > > > > SWIOTLB. > > > > > > > > The software IO TLB was designed with these assumptions: > > > > > > > > 1. It would not be used much, especially on 64-bit systems. > > > > 2. A small fixed memory area (64 MiB by default) is sufficient to > > > > handle the few cases which require a bounce buffer. > > > > 3. 64 MiB is little enough that it has no impact on the rest of the > > > > system. > > > > > > > > First, if SEV is active, all DMA must be done through shared > > > > unencrypted pages, and SWIOTLB is used to make this happen without > > > > changing device drivers. The software IO TLB size is increased to > > > > 6% of total memory in sev_setup_arch(), but that is more of an > > > > approximation. The actual requirements may vary depending on the > > > > amount of I/O and which drivers are used. These factors may not be > > > > know at boot time, i.e. when SWIOTLB is allocated. > > > > > > > > Second, other colleagues have noticed that they can reliably get > > > > rid of occasional OOM kills on an Arm embedded device by reducing > > > > the SWIOTLB size. This can be achieved with a kernel parameter, but > > > > determining the right value puts additional burden on pre-release > > > > testing, which could be avoided if SWIOTLB is allocated small and > > > > grows only when necessary. > > > > > > Now that merging into 6.4 has begun, what about this patch series? I'm > > > eager to get some feedback (positive or negative) and respin the next > > > version. > > > > It's the merge window, we can't add new things that haven't been in > > linux-next already. > > This is understood. I'm not asking for immediate inclusion. > > > Please resubmit it after -rc1 is out. > > If you can believe that rebasing to -rc1 will be enough, then I will > also try to believe I'm lucky. ;-) > > The kind of feedback I really want to get is e.g. about the extra > per-device DMA-specific fields. If they cannot be added to struct > device, then I'd rather start discussing an interim solution, because > getting all existing DMA fields out of that struct will take a lot of > time... I thought the goal was to get them out of the device and into the bus instead right? Or was it the other way around? I can't remember anymore, sorry... greg k-h