AVX-512 instruction set

AVX-512 instruction set

[Walid Ghandour]

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Hello,

I am interested in adding AVX512 to qemu.

Is anyone currently working on this ?

If yes, when is it expected to be done ?

I was trying to run a C program and failed with the following error at this
instruction:




*62 f2 7d 48 18 0d fa 0c 00 00 vbroadcastss 0xcfa(%rip),%zmm1qemu: uncaught
target signal 4 (Illegal instruction) - core dumped*
I like to add support for broadcast and fmadd avx 512 instructions such as
the following one:


*62 e2 7d 48 b8 c9     vfmadd231ps %zmm1,%zmm0,%zmm17*
Thanks,
Walid

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Re: AVX-512 instruction set

[Alex Bennée]

Walid Ghandour <waleedjghandour@gmail.com> writes:

> Hello,
>
> I am interested in adding AVX512 to qemu.

(add x86 TCG maintainers to CC)

> Is anyone currently working on this ?
>
> If yes, when is it expected to be done ?

I don't think there is currently any active effort to add AVX512
support. There have been various GSoC projects to improve the x86 SIMD
emulation but I don't think they got merged.

There has been some updates to improve the SSE emulation in the last few
releases and make the instruction decoder a little easier to work wit.

>
> I was trying to run a C program and failed with the following error at this instruction:
>
> 62 f2 7d 48 18 0d fa 0c 00 00 vbroadcastss 0xcfa(%rip),%zmm1
>
> qemu: uncaught target signal 4 (Illegal instruction) - core dumped
>
> I like to add support for broadcast and fmadd avx 512 instructions such as the following one: 
>
> 62 e2 7d 48 b8 c9     vfmadd231ps %zmm1,%zmm0,%zmm17
>
> Thanks,
> Walid


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro

Re: AVX-512 instruction set

[Paolo Bonzini]

On Wed, Apr 12, 2023 at 2:17 PM Alex Bennée <alex.bennee@linaro.org> wrote:
> I don't think there is currently any active effort to add AVX512
> support. There have been various GSoC projects to improve the x86 SIMD
> emulation but I don't think they got merged.

No, there isn't. However, the recent implementation of AVX in QEMU 7.2
is designed to make AVX512 at least doable.

Adding support for AVX512 would be a very large work (at least 1
months full time plus time to get it merged), but not impossible. The
tasks could be something like this:

1. EVEX prefix decoding for AVX and AVX2 instructions
2. operand broadcast
3. VEX encoded mask instruction: kmov, kadd, kxnor, etc
4. other instructions and permutations with mask operands and permutations
5. opmask support including merging and zeroing
6. Disp8*N addressing mode
7. rounding control and exception suppression

It's important that, at any given step, the new functionality is
tested comprehensively.

> > 62 f2 7d 48 18 0d fa 0c 00 00 vbroadcastss 0xcfa(%rip),%zmm1
> >
> > qemu: uncaught target signal 4 (Illegal instruction) - core dumped
> >
> > I like to add support for broadcast and fmadd avx 512 instructions such as the following one:
> >
> > 62 e2 7d 48 b8 c9     vfmadd231ps %zmm1,%zmm0,%zmm17

Both of these are using a small subset of AVX512 (step 1 above). Both
vbroadcastss and vfmadd231ps are already implemented in QEMU, but not
using ZMM registers.

Unfortunately the base AVX512 functionality is large, and therefore
the above tasks are all needed to claim support for AVX512. On the
other hand, for historical reasons AVX512BW and AVX512VL extensions
are separate but in practice they are easier to just implement at the
same time as basic AVX512; my expectation is that they would come up
almost for free with the rest of the work.

Paolo

Re: AVX-512 instruction set

[Walid Ghandour]

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I will try to work on this.

Regards,
Walid

Le mer. 12 avr. 2023 à 15:30, Paolo Bonzini <pbonzini@redhat.com> a écrit :

> On Wed, Apr 12, 2023 at 2:17 PM Alex Bennée <alex.bennee@linaro.org>
> wrote:
> > I don't think there is currently any active effort to add AVX512
> > support. There have been various GSoC projects to improve the x86 SIMD
> > emulation but I don't think they got merged.
>
> No, there isn't. However, the recent implementation of AVX in QEMU 7.2
> is designed to make AVX512 at least doable.
>
> Adding support for AVX512 would be a very large work (at least 1
> months full time plus time to get it merged), but not impossible. The
> tasks could be something like this:
>
> 1. EVEX prefix decoding for AVX and AVX2 instructions
> 2. operand broadcast
> 3. VEX encoded mask instruction: kmov, kadd, kxnor, etc
> 4. other instructions and permutations with mask operands and permutations
> 5. opmask support including merging and zeroing
> 6. Disp8*N addressing mode
> 7. rounding control and exception suppression
>
> It's important that, at any given step, the new functionality is
> tested comprehensively.
>
> > > 62 f2 7d 48 18 0d fa 0c 00 00 vbroadcastss 0xcfa(%rip),%zmm1
> > >
> > > qemu: uncaught target signal 4 (Illegal instruction) - core dumped
> > >
> > > I like to add support for broadcast and fmadd avx 512 instructions
> such as the following one:
> > >
> > > 62 e2 7d 48 b8 c9     vfmadd231ps %zmm1,%zmm0,%zmm17
>
> Both of these are using a small subset of AVX512 (step 1 above). Both
> vbroadcastss and vfmadd231ps are already implemented in QEMU, but not
> using ZMM registers.
>
> Unfortunately the base AVX512 functionality is large, and therefore
> the above tasks are all needed to claim support for AVX512. On the
> other hand, for historical reasons AVX512BW and AVX512VL extensions
> are separate but in practice they are easier to just implement at the
> same time as basic AVX512; my expectation is that they would come up
> almost for free with the rest of the work.
>
> Paolo
>
>

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Re: AVX-512 instruction set

[Paolo Bonzini]

On Wed, Apr 12, 2023 at 3:41 PM Walid Ghandour
<waleedjghandour@gmail.com> wrote:
> I will try to work on this.

Even if the individual tasks I listed are not enough to implement
AVX512, I suggest that you post individual pieces of work so that you
can somewhat pipeline the work.

Also, please review the design of the AVX decoder and the
implementation of the translation and the tests. You can find the
patches at https://patchew.org/QEMU/20221013214651.672114-1-pbonzini@redhat.com/
(patches 3-4-6-8 especially).

Paolo

> Regards,
> Walid
>
> Le mer. 12 avr. 2023 à 15:30, Paolo Bonzini <pbonzini@redhat.com> a écrit :
>>
>> On Wed, Apr 12, 2023 at 2:17 PM Alex Bennée <alex.bennee@linaro.org> wrote:
>> > I don't think there is currently any active effort to add AVX512
>> > support. There have been various GSoC projects to improve the x86 SIMD
>> > emulation but I don't think they got merged.
>>
>> No, there isn't. However, the recent implementation of AVX in QEMU 7.2
>> is designed to make AVX512 at least doable.
>>
>> Adding support for AVX512 would be a very large work (at least 1
>> months full time plus time to get it merged), but not impossible. The
>> tasks could be something like this:
>>
>> 1. EVEX prefix decoding for AVX and AVX2 instructions
>> 2. operand broadcast
>> 3. VEX encoded mask instruction: kmov, kadd, kxnor, etc
>> 4. other instructions and permutations with mask operands and permutations
>> 5. opmask support including merging and zeroing
>> 6. Disp8*N addressing mode
>> 7. rounding control and exception suppression
>>
>> It's important that, at any given step, the new functionality is
>> tested comprehensively.
>>
>> > > 62 f2 7d 48 18 0d fa 0c 00 00 vbroadcastss 0xcfa(%rip),%zmm1
>> > >
>> > > qemu: uncaught target signal 4 (Illegal instruction) - core dumped
>> > >
>> > > I like to add support for broadcast and fmadd avx 512 instructions such as the following one:
>> > >
>> > > 62 e2 7d 48 b8 c9     vfmadd231ps %zmm1,%zmm0,%zmm17
>>
>> Both of these are using a small subset of AVX512 (step 1 above). Both
>> vbroadcastss and vfmadd231ps are already implemented in QEMU, but not
>> using ZMM registers.
>>
>> Unfortunately the base AVX512 functionality is large, and therefore
>> the above tasks are all needed to claim support for AVX512. On the
>> other hand, for historical reasons AVX512BW and AVX512VL extensions
>> are separate but in practice they are easier to just implement at the
>> same time as basic AVX512; my expectation is that they would come up
>> almost for free with the rest of the work.
>>
>> Paolo
>>