Messages in this thread Patch in this message | | | Date | Fri, 26 Apr 2024 13:16:10 +0530 | Subject | Re: [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling | From | Shrikanth Hegde <> |
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On 4/23/24 9:43 PM, Linus Torvalds wrote: > On Tue, 23 Apr 2024 at 08:23, Shrikanth Hegde <sshegde@linux.ibm.com> wrote: >> >> >> Are these the only arch bits that need to be defined? am I missing something very >> basic here? will try to debug this further. Any inputs? > > I don't think powerpc uses the generic *_exit_to_user_mode() helper > functions, so you'll need to also add that logic to the low-level > powerpc code. > > IOW, on x86, with this patch series, patch 06/30 did this: > > - if (ti_work & _TIF_NEED_RESCHED) > + if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) > schedule(); > > in kernel/entry/common.c exit_to_user_mode_loop(). > > But that works on x86 because it uses the irqentry_exit_to_user_mode(). > > On PowerPC, I think you need to at least fix up > > interrupt_exit_user_prepare_main() > > similarly (and any other paths like that - I used to know the powerpc > code, but that was long long LOOONG ago). > > Linus
Thank you Linus for the pointers. That indeed did the trick.
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index eca293794a1e..f0f38bf5cea9 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -185,7 +185,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs) ti_flags = read_thread_flags(); while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) { local_irq_enable(); - if (ti_flags & _TIF_NEED_RESCHED) { + if (ti_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY) ) { schedule(); } else {
By adding LAZY checks in interrupt_exit_user_prepare_main, softlockup is no longer seen and hackbench results are more or less same on smaller system(96CPUS). However, I still see 20-50% regression on the larger system(320 CPUS). I will continue to debug why.
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