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Message-ID: <alpine.LSU.2.21.2109101130560.19415@pobox.suse.cz> Date: Fri, 10 Sep 2021 11:32:19 +0200 (CEST) From: Miroslav Benes <mbenes@...e.cz> To: Vasily Gorbik <gor@...ux.ibm.com> cc: Josh Poimboeuf <jpoimboe@...hat.com>, Jiri Kosina <jikos@...nel.org>, Petr Mladek <pmladek@...e.com>, Joe Lawrence <joe.lawrence@...hat.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Frederic Weisbecker <fweisbec@...il.com>, Thomas Gleixner <tglx@...utronix.de>, Heiko Carstens <hca@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>, Sumanth Korikkar <sumanthk@...ux.ibm.com>, live-patching@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] livepatch: Fix idle cpu's tasks transition 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@...ux.ibm.com> Seems reasonable to me. Acked-by: Miroslav Benes <mbenes@...e.cz> M
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