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From: Dave Martin <Dave.Martin@arm.com>
To: Andrea Bolognani <abologna@redhat.com>
Cc: "peter.maydell@linaro.org" <peter.maydell@linaro.org>,
	Andrew Jones <drjones@redhat.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"armbru@redhat.com" <armbru@redhat.com>,
	"qemu-arm@nongnu.org" <qemu-arm@nongnu.org>,
	"alex.bennee@linaro.org" <alex.bennee@linaro.org>
Subject: Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests
Date: Wed, 15 May 2019 12:14:20 +0100	[thread overview]
Message-ID: <20190515111420.GR28398@e103592.cambridge.arm.com> (raw)
In-Reply-To: <a24b6d34b99835ea38b021896a57c7af8bf4747c.camel@redhat.com>

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:
> > On 5/14/19 9:03 AM, Andrea Bolognani wrote:
> > > On Tue, 2019-05-14 at 14:53 +0200, Andrew Jones wrote:
> > > > We already have sve-max-vq, so I'm not sure we want to rename it.
> > > 
> > > Oh, I didn't realize that was the case. And of course it already
> > > takes a number of quadwords as argument, I suppose? That's pretty
> > > unfortunate :(
> > > 
> > > Perhaps we could consider deprecating it in favor of a user-friendly
> > > variant that's actually suitable for regular humans, like the one I
> > > suggest above?
> > 
> > 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.

Cheers
---Dave


  reply	other threads:[~2019-05-15 11:15 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-12  8:36 [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 01/13] target/arm/kvm64: fix error returns Andrew Jones
2019-06-05  7:20   ` Auger Eric
2019-05-12  8:36 ` [Qemu-devel] [PATCH 02/13] update-linux-headers: Add sve_context.h to asm-arm64 Andrew Jones
2019-06-05  7:21   ` Auger Eric
2019-06-05  7:30     ` Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 03/13] HACK: linux header update Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 04/13] target/arm/kvm: Move the get/put of fpsimd registers out Andrew Jones
2019-06-05  7:15   ` Auger Eric
2019-06-05  7:27     ` Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 05/13] target/arm/kvm: Add kvm_arch_get/put_sve Andrew Jones
2019-05-13 12:31   ` Dave Martin
2019-05-13 13:55     ` Andrew Jones
2019-05-13 15:31       ` Dave Martin
2019-05-13 15:40         ` Peter Maydell
2019-05-13 16:05           ` Dave Martin
2019-05-13 16:40     ` Richard Henderson
2019-05-13 18:14       ` Andrew Jones
2019-05-13 18:31         ` Richard Henderson
2019-05-13 12:43   ` Dave Martin
2019-05-13 14:07     ` Andrew Jones
2019-05-13 14:39       ` Dave Martin
2019-05-13 16:58         ` Richard Henderson
2019-05-14  9:10           ` Dave Martin
2019-05-12  8:36 ` [Qemu-devel] [PATCH 06/13] target/arm/kvm: max cpu: Enable SVE when available Andrew Jones
2019-06-05  9:09   ` Auger Eric
2019-06-05 11:04     ` Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 07/13] target/arm/kvm: max cpu: Allow sve max vector length setting Andrew Jones
2019-05-13 17:19   ` Richard Henderson
2019-05-13 18:19     ` Andrew Jones
2019-06-06  8:30   ` Auger Eric
2019-06-06  8:53     ` Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 08/13] target/arm/monitor: Add query-sve-vector-lengths Andrew Jones
2019-05-13 16:12   ` Markus Armbruster
2019-05-13 18:30     ` Andrew Jones
2019-05-14  5:32       ` Markus Armbruster
2019-05-12  8:36 ` [Qemu-devel] [PATCH 09/13] target/arm/kvm: Export kvm_arm_get_sve_vls Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 10/13] target/arm/monitor: kvm: only return valid sve vector sets Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 11/13] target/arm/cpu64: max cpu: Introduce sve-vls-map Andrew Jones
2019-05-13 11:26   ` Dave Martin
2019-05-13 12:30     ` Andrew Jones
2019-05-13 12:41       ` Dave Martin
2019-05-13 12:57         ` Andrew Jones
2019-05-13 13:12           ` Dave Martin
2019-05-13 13:45             ` Andrew Jones
2019-05-13 14:35               ` Dave Martin
2019-05-13 15:25   ` Markus Armbruster
2019-05-13 18:31     ` Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 12/13] target/arm/kvm: max cpu: Add support for sve-vls-map Andrew Jones
2019-05-12  8:36 ` [Qemu-devel] [PATCH 13/13] target/arm/kvm: host " Andrew Jones
2019-05-13 15:37   ` Markus Armbruster
2019-05-13 18:33     ` Andrew Jones
2019-05-13  9:32 ` [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests Andrea Bolognani
2019-05-13 11:15   ` Dave Martin
2019-05-13 12:38     ` Andrew Jones
2019-05-13 12:50       ` Dave Martin
2019-05-13 12:36   ` Andrew Jones
2019-05-14 12:29     ` Andrea Bolognani
2019-05-14 12:53       ` Andrew Jones
2019-05-14 16:03         ` Andrea Bolognani
2019-05-14 20:14           ` Richard Henderson
2019-05-15  8:03             ` Andrea Bolognani
2019-05-15 11:14               ` Dave Martin [this message]
2019-05-15 11:28                 ` Andrea Bolognani
2019-05-15 12:47                   ` Dave Martin
2019-05-15  9:15           ` Andrew Jones
2019-05-13  9:52 ` Peter Maydell
2019-05-13 12:43   ` Andrew Jones
2019-05-13 18:46 ` Richard Henderson
2019-05-13 19:16   ` Andrew Jones
2019-05-14  9:05   ` Peter Maydell

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