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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 22:24:06 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
Il 22/03/2013 20:20, Peter Lieven ha scritto:
>> 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 think you are right. I was a little to eager to utilize
> buffer_find_nonzero_offset()
> as much as possible. The performance gain by unrolling was impressive enough.
> The gain by the vector functions is not that big that it would justify a
> possible
> slow down by the high setup costs. My testings revealed that in most cases
> buffer_find_nonzero_offset()
> returns 0 or a big offset. All the 0 return values would have increased setup
> costs with
> the vectorized version of patch 4.
>
>>
>> I would prefer some more benchmarking for patch 5, but it looks ok.
> What would you like to see? Statistics how many pages of a real system
> are not zero, but zero in the first sizeof(long) bytes?
Yeah, more or less. Running the system for a while, migrating, and
plotting a histogram of the return values of buffer_find_nonzero_offset
(hmm, perhaps using a nonvectorized version is better for this experiment).
Paolo
- Re: [Qemu-devel] [PATCHv4 2/9] cutils: add a function to find non-zero content in a buffer, (continued)
[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, 2013/03/22
- 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 <=
- 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
- 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, 2013/03/26