| Message ID | alpine.DEB.2.21.1907171036490.1767@nanos.tec.linutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Avoid pointless schedule_preempt_irq() invocations | expand |
On 17/07/2019 09:43, Thomas Gleixner wrote: > When preempt_count is zero on return from interrupt then > schedule_preempt_irq() is invoked even if TIF_NEED_RESCHED is not set. > > That does not make sense because schedule_preempt_irq() has to go through a > full __schedule() for nothing in that case. > > Check TIF_NEED_RESCHED and invoke schedule_preempt_irq() only if set. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Don't we have NEED_RESCHED squashed into preempt count? 396244692232 ("arm64: preempt: Provide our own implementation of asm/preempt.h") So the existing check should cover that, unless I'm missing something? > --- > Found while staring at some RT wrecakge in that area. > --- > arch/arm64/kernel/entry.S | 4 ++++ > 1 file changed, 4 insertions(+) > > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -680,6 +680,10 @@ alternative_if ARM64_HAS_IRQ_PRIO_MASKIN > orr x24, x24, x0 > alternative_else_nop_endif > cbnz x24, 1f // preempt count != 0 || NMI return path > + > + ldr x0, [tsk, #TSK_TI_FLAGS] // get flags > + tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling? > + > bl preempt_schedule_irq // irq en/disable is done inside > 1: > #endif >
On Wed, 17 Jul 2019, Valentin Schneider wrote: > On 17/07/2019 09:43, Thomas Gleixner wrote: > > When preempt_count is zero on return from interrupt then > > schedule_preempt_irq() is invoked even if TIF_NEED_RESCHED is not set. > > > > That does not make sense because schedule_preempt_irq() has to go through a > > full __schedule() for nothing in that case. > > > > Check TIF_NEED_RESCHED and invoke schedule_preempt_irq() only if set. > > > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > > Don't we have NEED_RESCHED squashed into preempt count? > > 396244692232 ("arm64: preempt: Provide our own implementation of asm/preempt.h") > > So the existing check should cover that, unless I'm missing something? Right. Ignore me.
--- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -680,6 +680,10 @@ alternative_if ARM64_HAS_IRQ_PRIO_MASKIN orr x24, x24, x0 alternative_else_nop_endif cbnz x24, 1f // preempt count != 0 || NMI return path + + ldr x0, [tsk, #TSK_TI_FLAGS] // get flags + tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling? + bl preempt_schedule_irq // irq en/disable is done inside 1: #endif
When preempt_count is zero on return from interrupt then schedule_preempt_irq() is invoked even if TIF_NEED_RESCHED is not set. That does not make sense because schedule_preempt_irq() has to go through a full __schedule() for nothing in that case. Check TIF_NEED_RESCHED and invoke schedule_preempt_irq() only if set. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- Found while staring at some RT wrecakge in that area. --- arch/arm64/kernel/entry.S | 4 ++++ 1 file changed, 4 insertions(+)