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Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations
From: |
Peter Lieven |
Subject: |
Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations |
Date: |
Sat, 23 Mar 2013 08:34:40 +0100 |
Am 22.03.2013 um 22:24 schrieb Paolo Bonzini <address@hidden>:
> 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).
I will follow up with this on Monday. Have you seen my concern, that the whole
page is read anyway if it is non-zero?
Peter
>
> 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, 2013/03/22
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations,
Peter Lieven <=
- 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
- Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations, Paolo Bonzini, 2013/03/26