From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933660AbeB1RQm (ORCPT ); Wed, 28 Feb 2018 12:16:42 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:57066 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752679AbeB1RQl (ORCPT ); Wed, 28 Feb 2018 12:16:41 -0500 Date: Wed, 28 Feb 2018 19:16:35 +0200 From: "Michael S. Tsirkin" To: =?iso-8859-1?Q?Marc-Andr=E9?= Lureau Cc: Linux Kernel Mailing List , Sergio Lopez Pascual , Baoquan He , "Somlo, Gabriel" , xiaolong.ye@intel.com Subject: Re: [PATCH v15 11/11] RFC: fw_cfg: do DMA read operation Message-ID: <20180228191553-mutt-send-email-mst@kernel.org> References: <20180215213312.29234-1-marcandre.lureau@redhat.com> <20180215213312.29234-12-marcandre.lureau@redhat.com> <20180227020104-mutt-send-email-mst@kernel.org> <20180228173444-mutt-send-email-mst@kernel.org> <20180228174635-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 28, 2018 at 05:00:58PM +0100, Marc-André Lureau wrote: > Hi > > On Wed, Feb 28, 2018 at 4:48 PM, Michael S. Tsirkin wrote: > > On Wed, Feb 28, 2018 at 04:41:51PM +0100, Marc-André Lureau wrote: > >> I don't know if it's always safe to enable dma in read_raw(), how > >> could we know? Is there a check we could use to choose one or ther > >> other (and thus avoiding explicit dma/readfn argument)? > > > > I'm not sure - but does it really matter? Is anyone reading large files > > like this in production where speed matters? > > Why even bother with DMA? > > The difference is quite significante for not so small files, as shown above. > > And if they access the fw_cfg entries at boot time, or when starting > things etc, this may speed things up. Question would be whether anyone at all does this. -- MST