Re: [PATCH] powerpc: Add preempt lazy support
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: 2024-11-08 10:50:44
On 2024-11-08 15:48:53 [+0530], Shrikanth Hegde wrote:
Define preempt lazy bit for Powerpc. Use bit 9 which is free and within 16 bit range of NEED_RESCHED, so compiler can issue single andi. Since Powerpc doesn't use the generic entry/exit, add lazy check at exit to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for return to kernel. Ran a few benchmarks and db workload on Power10. Performance is close to preempt=none/voluntary. It is possible that some patterns would differ in lazy[2]. More details of preempt lazy is here [1] Since Powerpc system can have large core count and large memory, preempt lazy is going to be helpful in avoiding soft lockup issues. [1]: https://lore.kernel.org/lkml/20241007074609.447006177@infradead.org/ (local) [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/ (local)
The lazy bits are only in tip. Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
quoted hunk ↗ jump to hunk
Signed-off-by: Shrikanth Hegde <redacted> ---diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index af62ec974b97..8f4acc55407b 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c@@ -396,7 +396,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs) /* Returning to a kernel context with local irqs enabled. */ WARN_ON_ONCE(!(regs->msr & MSR_EE)); again: - if (IS_ENABLED(CONFIG_PREEMPT)) { + if (IS_ENABLED(CONFIG_PREEMPTION)) { /* Return to preemptible kernel context */ if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) { if (preempt_count() == 0)
Shouldn't exit_vmx_usercopy() get also this s@CONFIG_PREEMPT@CONFIG_PREEMPTION@ change ? Sebastian