Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753445AbaLALdc (ORCPT ); Mon, 1 Dec 2014 06:33:32 -0500 Received: from e06smtp17.uk.ibm.com ([195.75.94.113]:59242 "EHLO e06smtp17.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753035AbaLALda (ORCPT ); Mon, 1 Dec 2014 06:33:30 -0500 Date: Mon, 1 Dec 2014 12:33:15 +0100 From: Cornelia Huck To: "Michael S. Tsirkin" Cc: David Hildenbrand , linux-kernel@vger.kernel.org, David Miller , rusty@au1.ibm.com, nab@linux-iscsi.org, pbonzini@redhat.com, thuth@linux.vnet.ibm.com, Rusty Russell , virtualization@lists.linux-foundation.org, linux-api@vger.kernel.org Subject: Re: [PATCH v7 16/46] virtio_blk: v1.0 support Message-ID: <20141201123315.1b95d06f.cornelia.huck@de.ibm.com> In-Reply-To: <20141201092658.GC15607@redhat.com> References: <1417359787-10138-1-git-send-email-mst@redhat.com> <1417359787-10138-17-git-send-email-mst@redhat.com> <20141201091641.3085e682@thinkpad-w530> <20141201092658.GC15607@redhat.com> Organization: IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz =?UTF-8?B?R2VzY2jDpGZ0c2bDvGhydW5nOg==?= Dirk Wittkopp Sitz der Gesellschaft: =?UTF-8?B?QsO2Ymxpbmdlbg==?= Registergericht: Amtsgericht Stuttgart, HRB 243294 X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14120111-0029-0000-0000-000001F4E5A9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 1 Dec 2014 11:26:58 +0200 "Michael S. Tsirkin" wrote: > For some places on data path, it might be worth it > to cache the correct value e.g. as part of device > structure. This replaces a branch with a memory load, > so the gain would have to be measured, best done > separately? I think we'll want to do some measuring once the basic structure is in place anyway. We should make sure that e.g. s390 only takes minor hit due to all that swapping that is needed for standard-compliant devices. Caching the value might certainly help in some paths. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/