Re: [RFC][PATCH v2 00/21] x86/pti: Defer CR3 switch to C code

Borislav Petkov
2020-11-18T11:30:03Z

On Wed, Nov 18, 2020 at 08:41:42AM +0100, Alexandre Chartre wrote:
> Well, it looks like I wrongfully assume that KPTI was a well known performance
> overhead since it was introduced (because it adds extra page-table switches),
> but you are right I should be presenting my own numbers.

Here's one recipe, courtesy of Mel:

https://github.com/gormanm/mmtests

"
./run-mmtests.sh --no-monitor --config configs/config-workload-poundsyscall test-default

# reboot the machine with pti disabled

./run-mmtests.sh --no-monitor --config configs/config-workload-poundsyscall test-nopti

poundsyscall just calls getppid() so it's a light-weight syscall and a
proxy measure for syscall entry/exit costs. To do the actual compare

cd work/log
../../compare-kernels.sh

and see what gain there is from disabling pti. If you want to compare
the other direction

../../compare-kernels.sh --baseline test-nopti --compare test-default

If you get an error about BinarySearch

(echo y;echo o conf prerequisites_policy follow;echo o conf commit)|cpan
yes | cpan List::BinarySearch

Only se the second line if you want to interactively confirm what cpan
should download and install."

I've CCed him should you have any questions.

Thx.

--
Regards/Gruss,
Boris.