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 3581DC00140 for ; Fri, 5 Aug 2022 16:05:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241308AbiHEQF5 (ORCPT ); Fri, 5 Aug 2022 12:05:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43938 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241235AbiHEQFx (ORCPT ); Fri, 5 Aug 2022 12:05:53 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 89B8E402CA; Fri, 5 Aug 2022 09:05:51 -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 sin.source.kernel.org (Postfix) with ESMTPS id C4734CE2ABB; Fri, 5 Aug 2022 16:05:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C9298C433D7; Fri, 5 Aug 2022 16:05:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1659715548; bh=meLN3iFq0dB6/cRPWbxA3YaJYvQo+JhwHofyvaOjkjA=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=NbUpIVz3tIzfFG4V82gy2lgVrqrJgDHgNQKYqnqcc9wsh8f3ZCxDp8t9FlJDYylzv +Iu3a5h4Oa/48zEzWvJ5n7fxdlhFiaayxvOGAM5zduVXc1ew5pkQOhCIyGAheh+wto mECOAk/aaIKLCzR5MmhxOm+Z552Te38YesDwSMU1fG3u/gCBrGCxfL9anSCux5Irjg noqkXknHkKnRo3zvoeWuisCJfsbbCMEn5aaPr74JUaV9r1kY3/5YAMIxPnZqsCwjvh SrSvXLJziQ3ZRqApUsruuxrCVwbyFKklJ4dYx1zMJl1i/+XBwGXy+kTfIzRPME+C1I hI0cNl8b7GJPg== Date: Fri, 5 Aug 2022 11:05:45 -0500 From: Bjorn Helgaas To: "Arinzon, David" Cc: "linux-pci@vger.kernel.org" , "Dagan, Noam" , "Agroskin, Shay" , "Brandes, Shai" , "Kiyanovski, Arthur" , "mk@semihalf.com" , Alex Williamson , Cornelia Huck , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: vfio/pci - uAPI for WC Message-ID: <20220805160545.GA1020364@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org [+cc Alex, Cornelia, kvm, lkml (from "get_maintainer.pl drivers/vfio") and rewrapped for plain-text readability] On Thu, Aug 04, 2022 at 09:47:36AM +0000, Arinzon, David wrote: > Hi, > > There's currently no mechanism for vfio that exposes WC-related > operations (check if memory is WC capable, ask to WC memory) to user > space module entities, such as DPDK, for example. > > This topic has been previously discussed in [1], [2] and [3], but > there was no follow-up. > > This capability is very useful for DPDK, specifically to the DPDK > ENA driver that uses vfio-pci, which requires memory to be WC on the > TX path. Without WC, higher CPU utilization and performance > degradation are observed. > > In the above mentioned discussions, three options were suggested: > sysfs, ioctl, mmap extension (extra attributes). > > Was there any progress on this area? Is there someone who's looking > into this? > > We're leaning towards the ioctl option, if there are no objections, > we'd come up with an RFC. > [1]: https://patchwork.kernel.org/project/kvm/patch/20171009025000.39435-1-aik@ozlabs.ru/ > [2]: https://lore.kernel.org/linux-pci/2b539df4c9ec703458e46da2fc879ee3b310b31c.camel@kernel.crashing.org/ > [3]: https://lore.kernel.org/lkml/20210429162906.32742-2-sdonthineni@nvidia.com/ > > Thanks, > David