On Thu 2021-07-08 15:19:25, Vasily Gorbik wrote: > On Thu, Jul 08, 2021 at 12:35:24PM +0200, Petr Mladek wrote: > > On Wed 2021-07-07 14:49:41, Vasily Gorbik wrote: > > > 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
