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 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 45927C04E84 for ; Wed, 15 May 2019 11:29:34 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1C96C206BF for ; Wed, 15 May 2019 11:29:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1C96C206BF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:35465 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQs6H-0007E1-2T for qemu-devel@archiver.kernel.org; Wed, 15 May 2019 07:29:33 -0400 Received: from eggs.gnu.org ([209.51.188.92]:49731) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQs5E-0006o3-Dk for qemu-devel@nongnu.org; Wed, 15 May 2019 07:28:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hQs5D-0008L4-Cn for qemu-devel@nongnu.org; Wed, 15 May 2019 07:28:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49772) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hQs5B-0008Hh-1S; Wed, 15 May 2019 07:28:25 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 845C93078AD9; Wed, 15 May 2019 11:28:23 +0000 (UTC) Received: from kinshicho (unknown [10.43.2.73]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CEBD65D9DE; Wed, 15 May 2019 11:28:21 +0000 (UTC) Message-ID: <6ab7415d80419a7d9ac832b9194bf2d944696cd9.camel@redhat.com> From: Andrea Bolognani To: Dave Martin Date: Wed, 15 May 2019 13:28:20 +0200 In-Reply-To: <20190515111420.GR28398@e103592.cambridge.arm.com> References: <20190512083624.8916-1-drjones@redhat.com> <9f57bfa56715b3128c1823150457ddb866e6054c.camel@redhat.com> <20190513123656.6iu7ebu7zucn5mxt@kamzik.brq.redhat.com> <20190514125329.mi7ctaoujirwm6gs@kamzik.brq.redhat.com> <1857a74ef586a4e41d93b184498cfcf6c2927cec.camel@redhat.com> <1cd94ba6-2bfa-645e-1034-dd05e8a77000@linaro.org> <20190515111420.GR28398@e103592.cambridge.arm.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.32.2 (3.32.2-1.fc30) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Wed, 15 May 2019 11:28:23 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "peter.maydell@linaro.org" , Andrew Jones , Richard Henderson , "qemu-devel@nongnu.org" , "armbru@redhat.com" , "qemu-arm@nongnu.org" , "alex.bennee@linaro.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 2019-05-15 at 12:14 +0100, Dave Martin wrote: > On Wed, May 15, 2019 at 09:03:58AM +0100, Andrea Bolognani wrote: > > On Tue, 2019-05-14 at 13:14 -0700, Richard Henderson wrote: > > > Why is =4 less user-friendly than =512? > > > > > > I don't actually see "total bits in vector" as more user-friendly than "number > > > of quadwords" when it comes to non-powers-of-2 like =7 vs =896 or =13 vs =1664. > > > > I would wager most people are intimately familiar with bits, bytes > > and multiples due to having to work with them daily. Quadwords, not > > so much. > > Generally I tend to agree. For kvmtool I leaned torward quadwords > purely because > > 16,32,48,64,80,96,112,128,144,160,176,192,208 > > is a big pain to type compared with > > 1,2,3,4,5,6,7,8,9,10,11,12,13 > > Even though I prefer to specify vector lengths in bytes everywhere else > in the Linux user API (precisely to avoid the confusion you object to). > > This isn't finalised yet for kvmtool -- I need to rework the patches > and may not include it at all initially: kvmtool doesn't support > migration, which is the main usecase for being able to specify an exact > set of vector lengths AFAICT. > > Since this is otherwise only useful for migration, experimentation or > machine-driven configuration, a bitmask > > 0x1fff > > as some have suggested may well be a pragmatic alternative for kvmtool. Just to be clear, I have suggested using bits (or bytes or megabytes depending on the exact value) only for the command-line-user-oriented sve-vl-max option, which would take a single value. For interoperation with the management layer, on the other hand, using a bitmap is perfectly fine, and whether the values encoded within are expressed in quadwords or whatever other format is largely irrelevant, so long as it it's properly documented of course. -- Andrea Bolognani / Red Hat / Virtualization