Re: [Xen-devel] [Patch 0 of 2]: PV-domain SMP performance

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 17/12/2008 14:20, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxxxxxxx>
wrote:

> The advantage of my solution is a general mechanism to avoid preemption of
> a vcpu in critical sections instead of dealing with it after it has occured.
> Is the pv_ops Linux capable to deal with held locks in interrupt handling?
> What about other code paths which should be completed in short time?

Yes the approach is the other way round to yours. It handles irq-safe locks
just fine; no reason for it not to.

> About real world applications:
> Again 4 vcpus pinned to one physical cpu, 3 files copied via scp to the test
> machine at the same time, each file about 50 MB.
> 
> Linux-xen from xensource: about 1:50 elapsed time for each job
> My modified Linux:        about 0:50 elapsed time

So this provides great wins for those who run multi-vcpu VMs on a single
physical CPU? ;-) Actually getting a speedup on this benchmark even in that
configuration is a surprise I will admit -- I'd expect most time to be spent
in sshd in user space. By 0:50 for each job you mean 0:50 for 50MB? That's
10Mbps and I wouldn't even expect a single CPU working alone to be breaking
a sweat. Weird...

 -- Keir



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