Re: TLB evaluation for Linux

[Andi Kleen]

"CHADHA,VINEET" <vineet@xxxxxxx> writes:

> Hi,
>
> I have been working to evaluate TLB performance for Linux O/S and
> virtualized workloads(such as Xen) in a Full system
> simulator(e.g. simics). While my evaluation is in nascent stage, I do
> notice that most of the IPIs in multi-core environments cause complete
> TLB Flush.
>
> I want to evaluate cost of TLB shootdown including re-population
> vs. each entry shootdown (invlpg). While a similar study has been done
> in other kernels (e.g. L4 kernel), I am not aware if it has been done
> for Linux O/S.
>
> Are there hooks or patches to test or evaluate TLB
> performance. Specifically, I would like to know where to make changes
> in Linux kernel to support each entry shootdown.

Linux doesn't use a threshold to distingush between range flush
and full flush in certain situations, but always does the full
flush. 

That is something that might be possible to be improved, but it was so
far always unclear how much it helps (it depends on the particular TLB
size, cost of TLB refill etc.)

-Andi

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