| Message ID | 20170608153609.19217-2-npiggin@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 837e72f78a72ef43a0c5e179f3addadb2a225f80 |
| Headers | show |
Nicholas Piggin <npiggin@gmail.com> writes: > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 803c3bc274c4..1f0688ad09d7 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2875,6 +2875,12 @@ context_switch(struct rq *rq, struct task_struct *prev, > rq_unpin_lock(rq, rf); > spin_release(&rq->lock.dep_map, 1, _THIS_IP_); > > + /* > + * Some architectures require that a spin lock is taken before > + * _switch. The rq_lock satisfies this condition. See powerpc > + * _switch for details. > + */ > + > /* Here we just switch the register state and the stack. */ > switch_to(prev, next, prev); > barrier(); I dropped this hunk, if you want to merge it you can resend it and get an ack from Peterz. cheers
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 91f9fdc2d027..273a35926534 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -521,15 +521,10 @@ _GLOBAL(_switch) #endif /* CONFIG_SMP */ /* - * If we optimise away the clear of the reservation in system - * calls because we know the CPU tracks the address of the - * reservation, then we need to clear it here to cover the - * case that the kernel context switch path has no larx - * instructions. + * The kernel context switch path must contain a spin_lock, + * which contains larx/stcx, which will clear any reservation + * of the task being switched. */ -BEGIN_FTR_SECTION - ldarx r6,0,r1 -END_FTR_SECTION_IFSET(CPU_FTR_STCX_CHECKS_ADDRESS) BEGIN_FTR_SECTION /* diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 803c3bc274c4..1f0688ad09d7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2875,6 +2875,12 @@ context_switch(struct rq *rq, struct task_struct *prev, rq_unpin_lock(rq, rf); spin_release(&rq->lock.dep_map, 1, _THIS_IP_); + /* + * Some architectures require that a spin lock is taken before + * _switch. The rq_lock satisfies this condition. See powerpc + * _switch for details. + */ + /* Here we just switch the register state and the stack. */ switch_to(prev, next, prev); barrier();
There is no need to break reservation in _switch, because we are guranteed that context switch path will include a larx/stcx. Comment the guarantee and remove the reservation clear from _switch. This is worth 1-2% in context switch performance. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/kernel/entry_64.S | 11 +++-------- kernel/sched/core.c | 6 ++++++ 2 files changed, 9 insertions(+), 8 deletions(-)