Re: Performance of 40-way guest running 2.6.32-220 (RHEL6.2) vs. 3.3.1 OS

[Chegu Vinod <chegu_vinod@hp.com>]

Rik van Riel <riel <at> redhat.com> writes:

> 
> On 04/11/2012 01:21 PM, Chegu Vinod wrote:
> >
> > Hello,
> >
> > While running an AIM7 (workfile.high_systime) in a single 40-way (or a 
single
> > 60-way KVM guest) I noticed pretty bad performance when the guest was booted
> > with 3.3.1 kernel when compared to the same guest booted with 2.6.32-220
> > (RHEL6.2) kernel.
> 
> > For the 40-way Guest-RunA (2.6.32-220 kernel) performed nearly 9x better 
than
> > the Guest-RunB (3.3.1 kernel). In the case of 60-way guest run the older 
guest
> > kernel was nearly 12x better !
> 
> > Turned on function tracing and found that there appears to be more time 
being
> > spent around the lock code in the 3.3.1 guest when compared to the 2.6.32-
220
> > guest.
> 
> Looks like you may be running into the ticket spinlock
> code. During the early RHEL 6 days, Gleb came up with a
> patch to automatically disable ticket spinlocks when
> running inside a KVM guest.
> 

Thanks for the pointer. 
Perhaps that is the issue.  
I did look up that old discussion thread.


> IIRC that patch got rejected upstream at the time,
> with upstream developers preferring to wait for a
> "better solution".
> 
> If such a better solution is not on its way upstream
> now (two years later), maybe we should just merge
> Gleb's patch upstream for the time being?



Also noticed a recent discussion thread (that originated from the Xen context)

http://article.gmane.org/gmane.linux.kernel.virtualization/15078

Not yet sure if this recent discussion is also in some way related to
the older one initiated by Gleb.

Thanks
Vinod