Shrikanth Hegde <sshe...@linux.ibm.com> writes:
> 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/ > > Signed-off-by: Shrikanth Hegde <sshe...@linux.ibm.com> Looks good. Reviewed-by: <ankur.a.ar...@oracle.com> However, I just checked and powerpc does not have CONFIG_KVM_XFER_TO_GUEST_WORK. Do you need this additional patch for handling the lazy bit at KVM guest entry? diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c index f14329989e9a..7bdf7015bb65 100644 --- a/arch/powerpc/kvm/powerpc.c +++ b/arch/powerpc/kvm/powerpc.c @@ -84,7 +84,8 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu) hard_irq_disable(); while (true) { - if (need_resched()) { + unsigned long tf = read_thread_flags(); + if (tf & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) { local_irq_enable(); cond_resched(); hard_irq_disable(); Ankur
