On Thu, 9 Sep 2021, Vasily Gorbik wrote: > On an idle system with large amount of cpus it might happen that > klp_update_patch_state() is not reached in do_idle() for a long periods > of time. With debug messages enabled log is filled with: > [ 499.442643] livepatch: klp_try_switch_task: swapper/63:0 is running > > without any signs of progress. Ending up with "failed to complete > transition". > > On s390 LPAR with 128 cpus not a single transition is able to complete > and livepatch kselftests fail. Tests on idling x86 kvm instance with 128 > cpus demonstrate similar symptoms with and without CONFIG_NO_HZ. > > To deal with that, since runqueue is already locked in > klp_try_switch_task() identify idling cpus and trigger rescheduling > potentially waking them up and making sure idle tasks break out of > do_idle() inner loop and reach klp_update_patch_state(). This helps to > speed up transition time while avoiding unnecessary extra system load. > > Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx> Seems reasonable to me. Acked-by: Miroslav Benes <mbenes@xxxxxxx> M
