Re: [Qemu-devel] [PATCHv5 00/10] buffer_is_zero / migration optimizations

[Peter Lieven]

Am 26.03.2013 um 11:46 schrieb Juan Quintela <address@hidden>:

> Peter Lieven <address@hidden> wrote:
>> this is v5 of my patch series with various optimizations in
>> zero buffer checking and migration tweaks.
>> 
>> thanks especially to Eric Blake, Orit Wassermann and Paolo Bonzini
>> for reviewing.
>> 
>> v5:
>> - move zero splat vector to a different patch
>> - fix indentation of can_user_buffer_find_nonzero_offset()
>> - do not unroll the first loop in buffer_find_nonzero_offset()
>>  to optimize it for zero page checking
>> - use an older unrolled version of find_next_bit() without
>>  SIMD instruction as there is no evidence that the vectorized
>>  version is better if not even worse and the code is easier
>>  to understand.
>> - added a word in the commit message of patch 8 
>>  about the skipped pages field in QMP MigrationStats.
>> - fixed the order of key-value pairs of MigrationStats in
>>  qapi-schema.json
>> - updated info about the performance benefit of is_zero_page()
>>  to the latest benchmark results in the commit message.
>> 
>> v4:
>> - do not inline buffer_find_nonzero_offset()
>> - inline can_usebuffer_find_nonzero_offset() correctly
>> - readd asserts in buffer_find_nonzero_offset() as profiling
>>  shows they do not hurt.
>> - change last occurences of scalar 8 by 
>>  BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR
>> - avoid deferencing p already in patch 5 where we
>>  know that the page (p) is zero
>> - explicitly set bytes_sent = 0 if we skip a zero page.
>>  bytes_sent was 0 before, but it was not obvious.
>> - add accounting information for skipped zero pages
>> - fix errors reported by checkpatch.pl
>> 
>> v3:
>> - remove asserts, inline functions and add a check
>>  function if buffer_find_nonzero_offset() can be used.
>> - use above check function in buffer_is_zero() and
>>  find_next_bit().
>> - use buffer_is_nonzero_offset() directly to find
>>  zero pages. we know that all requirements are met
>>  for memory pages.
>> - fix C89 violation in buffer_is_zero().
>> - avoid derefencing p in ram_save_block() if we already
>>  know the page is zero.
>> - fix initialization of last_offset in reset_ram_globals().
>> - avoid skipping pages with offset == 0 in bulk stage in
>>  migration_bitmap_find_and_reset_dirty().
>> - compared to v1 check for zero pages also after bulk
>>  ram migration as there are guests (e.g. Windows) which
>>  zero out large amount of memory while running.
>> 
>> v2:
>> - fix description, add trivial zero check and add asserts 
>>  to buffer_find_nonzero_offset.
>> - add a constant for the unroll factor of buffer_find_nonzero_offset
>> - replace is_dup_page() by buffer_is_zero()
>> - added test results to xbzrle patch
>> - optimize descriptions
>> 
>> Peter Lieven (10):
>>  move vector definitions to qemu-common.h
>>  add a zero splat vector to qemu-common.h
>>  cutils: add a function to find non-zero content in a buffer
>>  buffer_is_zero: use vector optimizations if possible
>>  bitops: unroll while loop in find_next_bit()
>>  migration: search for zero instead of dup pages
>>  migration: add an indicator for bulk state of ram migration
>>  migration: do not sent zero pages in bulk stage
>>  migration: do not search dirty pages in bulk stage
>>  migration: use XBZRLE only after bulk stage
> 
> Really nice series.

Thank you.

> I did some minor review changes, but they are more nits that anynthing
> else.

Ok, where is your repository?

Peter


> 
> Thanks, Juan.
> 
> Reviewed-by: Juan Quintela <address@hidden>