Commit 00199ed6 authored by Shrikanth Hegde's avatar Shrikanth Hegde Committed by Madhavan Srinivasan
Browse files

powerpc: Add preempt lazy support 



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.

Since Powerpc systems can have large core count and large memory,
preempt lazy is going to be helpful in avoiding soft lockup issues.

Reviewed-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: default avatarAnkur Arora <ankur.a.arora@oracle.com>
Signed-off-by: default avatarShrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: default avatarMadhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20241116192306.88217-2-sshegde@linux.ibm.com
parent d629d7a8

arch/powerpc/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/powerpc/include/asm/thread_info.h

+6 −3
Original line number Diff line number Diff line
@@ -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 */

arch/powerpc/kernel/interrupt.c

+2 −2
Original line number Diff line number Diff line
@@ -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)