Re: [Xen-devel] Live migration: "netbuf race" messages can cause significant perfomance impact

[Steven Hand <Steven.Hand@xxxxxxxxxxxx>]

>Someone found that doing a live migration of a domain that had ballooned 
>down took far longer to migrate. (Ballooned down from 3000M to 1000M, 31 
>seconds vs 89 seconds, real time) I came up with a complex theory and 
>asked him to look in the xend.log to confirm it. He didn't, but he 
>mentioned there was a lot of "netbuf race" messages in the log. In this 
>particular case, live migration generated approximately 512000 "netbuf 
>race" messages. Deleting the DPRINTF reduced the migration time to 11 
>seconds.
>
>While it is simple enough to submit a patch to delete this DPRINTF, 
>perhaps something more subtle is called for such as modifying the 
>migrate/save command paths to accept a debug argument and passing to 
>xc_save?

There's nothing much we can do here - there's no easy way for us to 
distinguish between pages which are 'ballooned out' and pages which
are temporarily being used for network buffers. I've checked in a fix
to unstable (cset 13185:62ef527eb19f) which simply removes this particular
debug output.


thanks for spotting this! 

cheers,

S.


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