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From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Lieven <pl@kamp.de>
Cc: Orit Wasserman <owasserm@redhat.com>,
	quintela@redhat.com, qemu-devel@nongnu.org,
	Stefan Hajnoczi <stefanha@gmail.com>
Subject: Re: [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations
Date: Mon, 25 Mar 2013 09:02:02 -0400 (EDT)	[thread overview]
Message-ID: <972929461.13095041.1364216522903.JavaMail.root@redhat.com> (raw)
In-Reply-To: <CC5AC377-A8B1-4FD2-B249-8A27476D1ED6@kamp.de>

> Maybe I should have explained the output more detailed. The percentages
> are added. 35.8% in the second last column means that
> 35.8% have a return value that is less than TARGET_PAGE_SIZE.
> This was meant to illustrate at how many 64-bit chunks you have
> to look to grab a certain percentage of non-zero pages.

Ok, I wrongly understood that many pages had 4088 zero bytes but
the last 8 were not zero.  Now it's clearer, and more logical too. :)

> Looking e.g. at the third value it means that looking at the first
> three 64-bit chunks it will catch 34.0% of all pages.
> It turns out that the non-zeroness of a page can be detected looking
> at the first 256 or so bits and only a low
> percentage turns out to be non-zero at a later position. So after
> having checked the first chunks one by one
> there is no big penalty looking at the remaining chunks with the
> vectorized loop.

I think it makes most sense to unroll the first four non-vectorized
iterations, i.e. not use SSE and use three or four ifs.  Either:

   if (foo[0]) return 0;
   if (foo[1]) return 8;
   if (foo[2]) return 16;
   if (foo[3]) return 24;

or

   if (foo[0]) return 0;
   if (foo[1] | foo[2] | foo[3]) return 8;

and then proceed on the remaining 4096-4*sizeof(long) bytes with
the vectorized loop.  foo+4 is aligned for SIMD operations on both
32- and 64-bit machines, which makes this a nice choice.

Paolo

> Here is the distribution of return values for the Windows XP example:
> 
> 25.62% 0.49% 7.86% 0.12% 0.15% 0.05% 0.05% 0.04% 0.05% 0.02% 0.03%
> 0.02% 0.03% 0.02% 0.02% 0.01% 0.03% 0.02% 0.01% 0.02% 0.02% 0.01%
> 0.02% 0.01% 0.01% 0.01% 0.01% 0.01% 0.02% 0.00% 0.01% 0.02% 0.03%
> 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.00% 0.00% 0.01% 0.07% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.01% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.01% 0.02% 0.00% 0.00% 0.00%
> 0.00% 0.01% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.02% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.03% 0.00% 0.00% 0.00%
> 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.01%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.02% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.01%
> 0.00% 0.00% 0.00% 0.02% 0.00% 0.00% 0.02% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.01% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.01%
> 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
> 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 64.23%
> 
> The last value is the percentage of return value of TARGET_PAGE_SIZE
> meaning the page is all zero.
> 
> Peter
> 
> 

  reply	other threads:[~2013-03-25 13:02 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-03-22 12:46 [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations Peter Lieven
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 1/9] move vector definitions to qemu-common.h Peter Lieven
2013-03-25  8:35   ` Orit Wasserman
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 2/9] cutils: add a function to find non-zero content in a buffer Peter Lieven
2013-03-22 19:37   ` Eric Blake
2013-03-22 20:03     ` Peter Lieven
2013-03-22 20:22       ` [Qemu-devel] indentation hints [was: [PATCHv4 2/9] cutils: add a function to find non-zero content in a buffer] Eric Blake
2013-03-23 11:18         ` Peter Maydell
2013-03-25  8:53   ` [Qemu-devel] [PATCHv4 2/9] cutils: add a function to find non-zero content in a buffer Orit Wasserman
2013-03-25  8:56     ` Peter Lieven
2013-03-25  9:26       ` Orit Wasserman
2013-03-25  9:42         ` Paolo Bonzini
2013-03-25 10:03           ` Orit Wasserman
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 3/9] buffer_is_zero: use vector optimizations if possible Peter Lieven
2013-03-25  8:53   ` Orit Wasserman
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 4/9] bitops: use vector algorithm to optimize find_next_bit() Peter Lieven
2013-03-25  9:04   ` Orit Wasserman
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 5/9] migration: search for zero instead of dup pages Peter Lieven
2013-03-22 19:49   ` Eric Blake
2013-03-22 20:02     ` Peter Lieven
2013-03-25  9:30   ` Orit Wasserman
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 6/9] migration: add an indicator for bulk state of ram migration Peter Lieven
2013-03-25  9:32   ` Orit Wasserman
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 7/9] migration: do not sent zero pages in bulk stage Peter Lieven
2013-03-22 20:13   ` Eric Blake
2013-03-25  9:44   ` Orit Wasserman
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 8/9] migration: do not search dirty " Peter Lieven
2013-03-25 10:05   ` Orit Wasserman
2013-03-22 12:46 ` [Qemu-devel] [PATCHv4 9/9] migration: use XBZRLE only after " Peter Lieven
2013-03-25 10:16   ` Orit Wasserman
2013-03-22 17:25 ` [Qemu-devel] [PATCHv4 0/9] buffer_is_zero / migration optimizations Paolo Bonzini
2013-03-22 19:20   ` Peter Lieven
2013-03-22 21:24     ` Paolo Bonzini
2013-03-23  7:34       ` Peter Lieven
2013-03-25 10:17       ` Peter Lieven
2013-03-25 10:53         ` Paolo Bonzini
2013-03-25 11:26           ` Peter Lieven
2013-03-25 13:02             ` Paolo Bonzini [this message]
2013-03-25 13:23               ` Peter Lieven
2013-03-25 13:32                 ` Peter Lieven
2013-03-25 14:34                   ` Paolo Bonzini
2013-03-25 21:37                     ` Peter Lieven
2013-03-26  8:14                     ` Peter Lieven
2013-03-26  9:20                       ` Paolo Bonzini

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