| Message ID | 20241108101853.277808-1-sshegde@linux.ibm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | powerpc: Add preempt lazy support | expand |
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/ > [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/ The lazy bits are only in tip. Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Signed-off-by: Shrikanth Hegde <sshegde@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 ? Sebastian
Shrikanth Hegde <sshegde@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/20241007074609.447006177@infradead.org/ > [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/ > > Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com> Looks good. Reviewed-by: <ankur.a.arora@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
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 8094a01974cc..2f625aecf94b 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -145,6 +145,7 @@ config PPC select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE select ARCH_HAS_PHYS_TO_DMA select ARCH_HAS_PMEM_API + select ARCH_HAS_PREEMPT_LAZY select ARCH_HAS_PTE_DEVMAP if PPC_BOOK3S_64 select ARCH_HAS_PTE_SPECIAL select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64 diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h index 6ebca2996f18..2785c7462ebf 100644 --- a/arch/powerpc/include/asm/thread_info.h +++ b/arch/powerpc/include/asm/thread_info.h @@ -103,6 +103,7 @@ void arch_setup_new_exec(void); #define TIF_PATCH_PENDING 6 /* pending live patching update */ #define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */ #define TIF_SINGLESTEP 8 /* singlestepping active */ +#define TIF_NEED_RESCHED_LAZY 9 /* Scheduler driven lazy preemption */ #define TIF_SECCOMP 10 /* secure computing */ #define TIF_RESTOREALL 11 /* Restore all regs (implies NOERROR) */ #define TIF_NOERROR 12 /* Force successful syscall return */ @@ -122,6 +123,7 @@ void arch_setup_new_exec(void); #define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE) #define _TIF_SIGPENDING (1<<TIF_SIGPENDING) #define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED) +#define _TIF_NEED_RESCHED_LAZY (1<<TIF_NEED_RESCHED_LAZY) #define _TIF_NOTIFY_SIGNAL (1<<TIF_NOTIFY_SIGNAL) #define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG) #define _TIF_32BIT (1<<TIF_32BIT) @@ -142,9 +144,10 @@ void arch_setup_new_exec(void); _TIF_SYSCALL_EMU) #define _TIF_USER_WORK_MASK (_TIF_SIGPENDING | _TIF_NEED_RESCHED | \ - _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ - _TIF_RESTORE_TM | _TIF_PATCH_PENDING | \ - _TIF_NOTIFY_SIGNAL) + _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_RESUME | \ + _TIF_UPROBE | _TIF_RESTORE_TM | \ + _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL) + #define _TIF_PERSYSCALL_MASK (_TIF_RESTOREALL|_TIF_NOERROR) /* Bits in local_flags */ 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 @@ -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 { /* @@ -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)
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/ [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/ Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com> --- arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/thread_info.h | 9 ++++++--- arch/powerpc/kernel/interrupt.c | 4 ++-- 3 files changed, 9 insertions(+), 5 deletions(-)