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Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests
From: |
Andrea Bolognani |
Subject: |
Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests |
Date: |
Wed, 15 May 2019 13:28:20 +0200 |
User-agent: |
Evolution 3.32.2 (3.32.2-1.fc30) |
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
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, (continued)
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Andrew Jones, 2019/05/13
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Andrea Bolognani, 2019/05/14
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Andrew Jones, 2019/05/14
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Andrea Bolognani, 2019/05/14
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Richard Henderson, 2019/05/14
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Andrea Bolognani, 2019/05/15
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Dave Martin, 2019/05/15
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests,
Andrea Bolognani <=
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Dave Martin, 2019/05/15
- Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Andrew Jones, 2019/05/15
Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Peter Maydell, 2019/05/13
Re: [Qemu-devel] [PATCH 00/13] target/arm/kvm: enable SVE in guests, Richard Henderson, 2019/05/13