Re: kvm_read() vs ioctl performance

Barney Cordoba wrote:
--- Julian Elischer <julian@xxxxxxxxxxxx> wrote:

Barney Cordoba wrote:
I have an app which reads stats from the kernel
periodically, and there can be a lot of
iterations,
sometimes 20,000 or more. I'm thinking of
converting
from an ioctl method to kvm_read(). KVM is
certainly
simpler, but its not clear what overhead is
involved,
since kvm_read() likely has to call the kernel
also.
Does anyone have a handle on the difference in
overhead, assuming that the ioctl call is to a
module
which does nothing more than copy the data and
return?

tried a shared memory page?

No, but I built a test and kvm_read is 70 times
faster, in
case anyone is interested.

cool..
the only downside is that we are trying to get away from kvm direct access. (which is why a shared page might give the same result with a stable API which is not libkvm... BTW on an SMP machine you have
no way to ensure that your stats are coherent if you use libkvm.



Barney


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