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Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations |
Date: |
Fri, 22 Mar 2013 18:25:39 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
Il 22/03/2013 13:46, Peter Lieven ha scritto:
> this is v4 of my patch series with various optimizations in
> zero buffer checking and migration tweaks.
>
> thanks especially to Eric Blake for reviewing.
>
> 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 (9):
> move vector definitions 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: use vector algorithm to optimize 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
>
> arch_init.c | 74
> +++++++++++++++++++----------------------
> hmp.c | 2 ++
> include/migration/migration.h | 2 ++
> include/qemu-common.h | 37 +++++++++++++++++++++
> migration.c | 3 +-
> qapi-schema.json | 6 ++--
> qmp-commands.hx | 3 +-
> util/bitops.c | 24 +++++++++++--
> util/cutils.c | 50 ++++++++++++++++++++++++++++
> 9 files changed, 155 insertions(+), 46 deletions(-)
>
I think patch 4 is a bit overengineered. I would prefer the simple
patch you had using three/four non-vectorized accesses. The setup cost
of the vectorized buffer_is_zero is quite high, and 64 bits are just
256k RAM; if the host doesn't touch 256k RAM, it will incur the overhead.
I would prefer some more benchmarking for patch 5, but it looks ok.
The rest are fine, thanks!
Paolo
- [Qemu-devel] indentation hints [was: [PATCHv4 2/9] cutils: add a function to find non-zero content in a buffer], (continued)
Re: [Qemu-devel] [PATCHv4 2/9] cutils: add a function to find non-zero content in a buffer, Orit Wasserman, 2013/03/25
[Qemu-devel] [PATCHv4 7/9] migration: do not sent zero pages in bulk stage, Peter Lieven, 2013/03/22
Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Peter Lieven, 2013/03/22
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Paolo Bonzini, 2013/03/22
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Peter Lieven, 2013/03/23
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Peter Lieven, 2013/03/25
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Paolo Bonzini, 2013/03/25
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Peter Lieven, 2013/03/25
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Paolo Bonzini, 2013/03/25
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Peter Lieven, 2013/03/25
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Peter Lieven, 2013/03/25
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Paolo Bonzini, 2013/03/25