Thank you Sebastian for taking a look and rwb tag.
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/20241007074609.447006...@infradead.org/
[2]:
https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb07...@linux.ibm.com/
The lazy bits are only in tip.
Hi Michael, I sent it to powerpc tree since all the changes were in
arch/powerpc. Please let me know if i have send it to tip tree instead.
Reviewed-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
Signed-off-by: Shrikanth Hegde <sshe...@linux.ibm.com>
---
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 ?
I had seen this, but wasn't sure. Will take a look at it.
Thanks for the pointers.
Sebastian
