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Re: [Qemu-devel] slow xbzrle
From: |
Orit Wasserman |
Subject: |
Re: [Qemu-devel] slow xbzrle |
Date: |
Thu, 25 Oct 2012 13:39:13 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 |
On 10/25/2012 12:35 PM, Stefan Priebe - Profihost AG wrote:
> Am 25.10.2012 11:44, schrieb Orit Wasserman:
>>> Is this known or is something wrong?
>> My guess this workload migrates fine without XBZRLE so it is not the speed
>> or downtime :).
>> it could be that the cache size is too small resulting with a lot of cache
>> misses which means
>> XBZRLE makes things worse and just uses CPU to maintain the cache.
>> Other option is that this workload changes the pages too much which can
>> result with a lot of over flows
>> which result in XBZRLE to waste CPU scanning the pages.
>> As this is idle mysql my guess it the first scenario.
>>
>> Can you send the cache size, cache miss and overflow (from 'info migrate')?
>
> Example got from a log file (it's the info from info migrate just in another
> format):
> migration xbzrle
> cachesize: 1073741824
> transferred 0
> pages 0
> cachemiss 1315374
Looks like a lot of cache miss, you can try increasing the cache size
(migrate_set_cache_size).
But you should remember that for an idle guest XBZRLE is wasteful,
it is useful for workload that changes the same memory pages frequently.
Orit
> overflow 0
>
> Stefan