RE: [Xen-devel] [PATCH] permute with 2MB chunk

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

Also a bit curious whether original intent of permute() still keeps 
true on a 2M granularity from this good patch:

    /* Need a simple permutation function so that we scan pages in a
       pseudo random order, enabling us to get a better estimate of
       the domain's page dirtying rate as we go (there are often
       contiguous ranges of pfns that have similar behaviour, and we
       want to mix them up. */

And if not, maybe permute() can be removed instead, or with some
counterpart in restore side? :-)

Thanks,
Kevin
>From: Cui, Dexuan
>Sent: 2008年3月19日 17:42
>
>Hi Jean,
>The patch does fix the bug. Great!
>
>I made a test to change xc_hvm_build() to invoke 
>xc_domain_memory_populate_physmap() in the same pfn order of 
>that in the old permute(); then I created an HVM guest, and I 
>met with almost the same slowness in it!
>Looks the old poor version of permute() can incur high rate of 
>cache miss, hence the slowness after S/R is caused?
>
>However, I still have questions:
>For the bug, I remember the slowness 
>1) Only happens to HVM guest (PV-guest has not this issue);   
>-- any difference between HVM and PV here??
>2) Only happens to S/R and local non-live migration, but 
>doesn't happen to local live migration. -- any difference 
>between live and non-live here??
>And when we suffer from the slowness, "local live migrating" 
>the HVM guest can make the performance back to normal!
>
>Can you reproduce these in your side? If so, can you help to 
>explain them? 
>
>Many thanks!
>
>-- Dexuan
>
>
>-----Original Message-----
>From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
>[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
>Jean Guyader
>Sent: 2008年3月19日 2:03
>To: xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: [Xen-devel] [PATCH] permute with 2MB chunk
>
>
>The memory permutation cause a slow down in case of a 
>save/restore (bug 
>1143). It works better when the mixing is done with 2MB chunks.
>
>Signed-off-by: Jean Guyader <jean.guyader@xxxxxxxxxxxxx>
>
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