Re: KVM performance vs. Xen

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Avi Kivity wrote:
Anthony Liguori wrote:

Previously, the block API only exposed non-vector interfaces and bounced vectored operations to a linear buffer. That's been eliminated now though so we need to update the linux-aio patch to implement a vectored backend interface.

However, it is an apples to apples comparison in terms of copying since the same is true with the thread pool. My take away was that the thread pool overhead isn't the major source of issues.

If the overhead is dominated by copying, then you won't see the difference. Once the copying is eliminated, the comparison may yield different results. We should certainly see a difference in context switches.

Yes, I agree with this. The absence of copying (in both the thread pool and linux-aio) could yield significantly different results.

Regards,

Anthony Liguori

One cause of context switches won't be eliminated - the non-saturating workload causes us to switch to the idle thread, which incurs a heavyweight exit. This doesn't matter since we're idle anyway, but when we switch back, we incur a heavyweight entry.


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