Re: [Qemu-devel] QEmu TCG SIMD extension?

[Paolo Bonzini <pbonzini@redhat.com>]

Il 06/03/2013 04:47, Peter Maydell ha scritto:
> On 6 March 2013 11:30, 陳韋任 (Wei-Ren Chen) <chenwj@iis.sinica.edu.tw> wrote:
>> While searching for QEMU SIMD issues, I found there was a paper presented
>> in 2011 [1], and the source code is also public on [2]. However, it seems
>> this project doesn't make any progress since last year. I update their
>> change to upstream and you can download from here:
>>
>>   $ git clone git://github.com/azru0512/qemu.git -b neon-simd
>>
>> Sadly, it can not boot the kernel image provided on [2]. Anyway, I
>> found there was only one thread has discussion on their work [3]. I want
>> to hear more feedback on their idea on adding SIMD TCG IR.
> 
> I think my opinions are still the same -- interesting idea, but getting
> it to work with a set of IR ops which aren't target or host specific
> and getting it to give correct bit-for-bit results, rounding, flags,
> etc, is likely to be tricky. It would also be important to determine
> first whether Neon (or other SIMD) emulation performance is truly
> a major bottleneck.

SSE operations, while not a bottleneck, are the top helpers in the
profile when booting Linux on x86.

Using common code to generate the simplest unrolled SIMD operations
(logical operations, add, subtract, compare to zero) would already help
a lot, I think.

Paolo