On Thu 2021-07-08 15:19:25, Vasily Gorbik wrote:

On Thu, Jul 08, 2021 at 12:35:24PM +0200, Petr Mladek wrote:

quoted

On Wed 2021-07-07 14:49:41, Vasily Gorbik wrote:

quoted

That's just a racy hack for now for demonstration purposes.

For s390 LPAR with 128 cpu this reduces livepatch kselftest run time
from
real    1m11.837s
user    0m0.603s
sys     0m10.940s

to
real    0m14.550s
user    0m0.420s
sys     0m5.779s

Would smth like that be useful for production use cases?
Any ideas how to approach that more gracefully?

Honestly, I do not see a real life use case for this, except maybe
speeding up a test suite.

The livepatch transition is more about reliability than about speed.
In the real life, a livepatch will be applied only once in a while.

That's what I thought. Thanks for looking. Dropping this one.

If you still wanted to speed up the transition from some reason
then an easy win might be to call klp_send_signals() earlier.

Well, my view is the following. The primary livepatching task is
to fix some broken/vulnerable functionality on a running kernel.
It should ideally happen on background and do not affect or slow
down the existing work load.

klp_send_signals() is not ideal. The fake signal interrupts syscalls
and they need to get restarted. Also the function wakes up a lot of
tasks and might increase load. Hence, it is used as a last resort that
allows to finish the transition in a reasonable time frame.

That said, the current timeouts are arbitrary chosen values based
rather on a common sense than on some measurement. I could imagine that
we could modify them or allow to trigger klp_send_signal() via
sysfs when there is a good reason.

Best Regards,
Petr