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xen-devel
Re: [Xen-devel] open/stat64 syscalls run faster on Xen VM than standard
xuehai zhang wrote:
So, the benchmark experiments I've done so far suggests XenLinux using
loopback files as VBD backends shows better performance (faster
execution) on part of the system calls like open and stat64, but it
shows worse performance (slower execution) on other system calls like
write than the standard Linux. Does this mean different applications
may have different execution behaviors on VM than on the standard
Linux? In other words, some applications run faster on VM and some
slower, comparing with the physical machine?
I really want to stress here that your results do not mean system calls
are faster in Xen (or with a loopback device). You're seeing the
effects of caching which are probably sub-optimal for overall performance.
A more meaningful benchmark here is to take a syscall intensive
workload, and measure the thoroughput. You'll likely find that the
syscall performance is actually worse because when you start missing the
cache you're going to get huge delays in read-ahead.
Be wary of microbenchmarks, they often are way off from real-world
scenarios.
As for write performance, in general, read and write performance are
going to be measurably slower in Xen than on bare-metal Linux. It
almost has to be by definition. The hope is that the difference in
performance will be neglible especially considering the improved
thoroughput from greater utiliziation of the underlying hardware.
Regards,
Anthony Liguori
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