Re: [Qemu-devel] [PATCH v5 0/2] add avx2 instruction optimization

[Paolo Bonzini <pbonzini@redhat.com>]

On 27/01/2016 08:33, Liang Li wrote:
> buffer_find_nonzero_offset() is a hot function during live migration.
> Now it use SSE2 instructions for optimization. For platform supports
> AVX2 instructions, use the AVX2 instructions for optimization can help
> to improve the performance of zero page checking about 30% comparing
> to SSE2.
> Live migration can be faster with this optimization, the test result
> shows that for an 8GB RAM idle guest, this patch can help to shorten
> the total live migration time about 6%.
> 
> This patch use the ifunc mechanism to select the proper function when
> running, for platform supports AVX2, execute the AVX2 instructions,
> else, execute the original instructions.
> 
> With this patch, the QEMU binary can run on both platforms support AVX2
> or not.
> 
> Compiler which doesn't support the AVX2 and ifunc attribute can also build
> the source code successfully.
> 
> v5 -> v4 changes:
>   * Enhance the ifunc attribute detection (Paolo's suggestion)
> 
> v3 -> v4 changes:
>   * Use the GCC #pragma to make things simple (Paolo's suggestion) 
>   * Put avx2 related code in cutils.c (Richard's suggestion)
>   * Change the configure, detect ifunc and avx2 attributes together
> 
> v2 -> v3 changes:
>   * Detect the ifunc attribute support (Paolo's suggestion) 
>   * Use the ifunc attribute instead of the inline asm (Richard's suggestion)
>   * Change the configure (Juan's suggestion)
> 
> Liang Li (2):
>   configure: detect ifunc and avx2 attribute
>   cutils: add avx2 instruction optimization
> 
>  configure             |  21 +++++++++
>  include/qemu-common.h |   8 +---
>  util/cutils.c         | 118 ++++++++++++++++++++++++++++++++++++++++++++++++--
>  3 files changed, 136 insertions(+), 11 deletions(-)

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>