* [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT) @ 2017-10-06 17:19 ` Jason Baron 2017-10-06 18:36 ` Jacob Pan 0 siblings, 1 reply; 4+ messages in thread From: Jason Baron @ 2017-10-06 17:19 UTC (permalink / raw) To: linux-pm, linux-kernel; +Cc: Jacob Pan, Len Brown, Rafael J. Wysocki If the 'arat' cpu flag is set, then the conditionals in intel_idle() that guard calling tick_broadcast_enter()/exit() will never be true. Use static_cpu_has(X86_FEATURE_ARAT) to create a fast path to replace the conditional. Signed-off-by: Jason Baron <jbaron@akamai.com> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com> Cc: Len Brown <lenb@kernel.org> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> --- drivers/idle/intel_idle.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index 5dc7ea4..5db5e31 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -913,8 +913,7 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev, struct cpuidle_state *state = &drv->states[index]; unsigned long eax = flg2MWAIT(state->flags); unsigned int cstate; - - cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1; + bool uninitialized_var(tick); /* * NB: if CPUIDLE_FLAG_TLB_FLUSHED is set, this idle transition @@ -923,12 +922,19 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev, * useful with this knowledge. */ - if (!(lapic_timer_reliable_states & (1 << (cstate)))) - tick_broadcast_enter(); + if (!static_cpu_has(X86_FEATURE_ARAT)) { + cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & + MWAIT_CSTATE_MASK) + 1; + tick = false; + if (!(lapic_timer_reliable_states & (1 << (cstate)))) { + tick = true; + tick_broadcast_enter(); + } + } mwait_idle_with_hints(eax, ecx); - if (!(lapic_timer_reliable_states & (1 << (cstate)))) + if (!static_cpu_has(X86_FEATURE_ARAT) && tick) tick_broadcast_exit(); return index; -- 2.6.1 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT) 2017-10-06 17:19 ` [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT) Jason Baron @ 2017-10-06 18:36 ` Jacob Pan 2017-10-06 18:41 ` Jason Baron 0 siblings, 1 reply; 4+ messages in thread From: Jacob Pan @ 2017-10-06 18:36 UTC (permalink / raw) To: Jason Baron; +Cc: linux-pm, linux-kernel, jacob.jun.pan On Fri, 6 Oct 2017 13:19:45 -0400 Jason Baron <jbaron@akamai.com> wrote: > If the 'arat' cpu flag is set, then the conditionals in intel_idle() > that guard calling tick_broadcast_enter()/exit() will never be true. > Use static_cpu_has(X86_FEATURE_ARAT) to create a fast path to replace > the conditional. > > Signed-off-by: Jason Baron <jbaron@akamai.com> > Cc: Jacob Pan <jacob.jun.pan@linux.intel.com> > Cc: Len Brown <lenb@kernel.org> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > --- > drivers/idle/intel_idle.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c > index 5dc7ea4..5db5e31 100644 > --- a/drivers/idle/intel_idle.c > +++ b/drivers/idle/intel_idle.c > @@ -913,8 +913,7 @@ static __cpuidle int intel_idle(struct > cpuidle_device *dev, struct cpuidle_state *state = > &drv->states[index]; unsigned long eax = flg2MWAIT(state->flags); > unsigned int cstate; > - > - cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & > MWAIT_CSTATE_MASK) + 1; > + bool uninitialized_var(tick); > > /* > * NB: if CPUIDLE_FLAG_TLB_FLUSHED is set, this idle > transition @@ -923,12 +922,19 @@ static __cpuidle int > intel_idle(struct cpuidle_device *dev, > * useful with this knowledge. > */ > > - if (!(lapic_timer_reliable_states & (1 << (cstate)))) > - tick_broadcast_enter(); > + if (!static_cpu_has(X86_FEATURE_ARAT)) { > + cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & > + MWAIT_CSTATE_MASK) + 1; > + tick = false; > + if (!(lapic_timer_reliable_states & (1 << > (cstate)))) { > + tick = true; > + tick_broadcast_enter(); > + } > + } > > mwait_idle_with_hints(eax, ecx); > > - if (!(lapic_timer_reliable_states & (1 << (cstate)))) > + if (!static_cpu_has(X86_FEATURE_ARAT) && tick) > tick_broadcast_exit(); > > return index; Seems better to have a function pointer set up at init time to select whether we do tick_broadcast or not (two functions). There is no need to check CPU feature on every entry. ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT) 2017-10-06 18:36 ` Jacob Pan @ 2017-10-06 18:41 ` Jason Baron 2017-10-06 21:09 ` Jacob Pan 0 siblings, 1 reply; 4+ messages in thread From: Jason Baron @ 2017-10-06 18:41 UTC (permalink / raw) To: Jacob Pan; +Cc: linux-pm, linux-kernel On 10/06/2017 02:36 PM, Jacob Pan wrote: > On Fri, 6 Oct 2017 13:19:45 -0400 > Jason Baron <jbaron@akamai.com> wrote: > >> If the 'arat' cpu flag is set, then the conditionals in intel_idle() >> that guard calling tick_broadcast_enter()/exit() will never be true. >> Use static_cpu_has(X86_FEATURE_ARAT) to create a fast path to replace >> the conditional. >> >> Signed-off-by: Jason Baron <jbaron@akamai.com> >> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com> >> Cc: Len Brown <lenb@kernel.org> >> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> --- >> drivers/idle/intel_idle.c | 16 +++++++++++----- >> 1 file changed, 11 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c >> index 5dc7ea4..5db5e31 100644 >> --- a/drivers/idle/intel_idle.c >> +++ b/drivers/idle/intel_idle.c >> @@ -913,8 +913,7 @@ static __cpuidle int intel_idle(struct >> cpuidle_device *dev, struct cpuidle_state *state = >> &drv->states[index]; unsigned long eax = flg2MWAIT(state->flags); >> unsigned int cstate; >> - >> - cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & >> MWAIT_CSTATE_MASK) + 1; >> + bool uninitialized_var(tick); >> >> /* >> * NB: if CPUIDLE_FLAG_TLB_FLUSHED is set, this idle >> transition @@ -923,12 +922,19 @@ static __cpuidle int >> intel_idle(struct cpuidle_device *dev, >> * useful with this knowledge. >> */ >> >> - if (!(lapic_timer_reliable_states & (1 << (cstate)))) >> - tick_broadcast_enter(); >> + if (!static_cpu_has(X86_FEATURE_ARAT)) { >> + cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & >> + MWAIT_CSTATE_MASK) + 1; >> + tick = false; >> + if (!(lapic_timer_reliable_states & (1 << >> (cstate)))) { >> + tick = true; >> + tick_broadcast_enter(); >> + } >> + } >> >> mwait_idle_with_hints(eax, ecx); >> >> - if (!(lapic_timer_reliable_states & (1 << (cstate)))) >> + if (!static_cpu_has(X86_FEATURE_ARAT) && tick) >> tick_broadcast_exit(); >> >> return index; > > Seems better to have a function pointer set up at init time to select > whether we do tick_broadcast or not (two functions). There is no need to > check CPU feature on every entry. > Hi, static_cpu_has() uses alternatives patching, so the cpu feature is not tested on every entry. With the arat flag set you just have two nops in the straight-line code path with this patch. Thanks, -Jason ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT) 2017-10-06 18:41 ` Jason Baron @ 2017-10-06 21:09 ` Jacob Pan 0 siblings, 0 replies; 4+ messages in thread From: Jacob Pan @ 2017-10-06 21:09 UTC (permalink / raw) To: Jason Baron; +Cc: linux-pm, linux-kernel, jacob.jun.pan On Fri, 6 Oct 2017 14:41:07 -0400 Jason Baron <jbaron@akamai.com> wrote: > On 10/06/2017 02:36 PM, Jacob Pan wrote: > > On Fri, 6 Oct 2017 13:19:45 -0400 > > Jason Baron <jbaron@akamai.com> wrote: > > > >> If the 'arat' cpu flag is set, then the conditionals in > >> intel_idle() that guard calling tick_broadcast_enter()/exit() will > >> never be true. Use static_cpu_has(X86_FEATURE_ARAT) to create a > >> fast path to replace the conditional. > >> > >> Signed-off-by: Jason Baron <jbaron@akamai.com> > >> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com> > >> Cc: Len Brown <lenb@kernel.org> > >> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > >> --- > >> drivers/idle/intel_idle.c | 16 +++++++++++----- > >> 1 file changed, 11 insertions(+), 5 deletions(-) > >> > >> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c > >> index 5dc7ea4..5db5e31 100644 > >> --- a/drivers/idle/intel_idle.c > >> +++ b/drivers/idle/intel_idle.c > >> @@ -913,8 +913,7 @@ static __cpuidle int intel_idle(struct > >> cpuidle_device *dev, struct cpuidle_state *state = > >> &drv->states[index]; unsigned long eax = flg2MWAIT(state->flags); > >> unsigned int cstate; > >> - > >> - cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & > >> MWAIT_CSTATE_MASK) + 1; > >> + bool uninitialized_var(tick); > >> > >> /* > >> * NB: if CPUIDLE_FLAG_TLB_FLUSHED is set, this idle > >> transition @@ -923,12 +922,19 @@ static __cpuidle int > >> intel_idle(struct cpuidle_device *dev, > >> * useful with this knowledge. > >> */ > >> > >> - if (!(lapic_timer_reliable_states & (1 << (cstate)))) > >> - tick_broadcast_enter(); > >> + if (!static_cpu_has(X86_FEATURE_ARAT)) { > >> + cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & > >> + MWAIT_CSTATE_MASK) + 1; > >> + tick = false; > >> + if (!(lapic_timer_reliable_states & (1 << > >> (cstate)))) { > >> + tick = true; > >> + tick_broadcast_enter(); > >> + } > >> + } > >> > >> mwait_idle_with_hints(eax, ecx); > >> > >> - if (!(lapic_timer_reliable_states & (1 << (cstate)))) > >> + if (!static_cpu_has(X86_FEATURE_ARAT) && tick) > >> tick_broadcast_exit(); > >> > >> return index; > > > > Seems better to have a function pointer set up at init time to > > select whether we do tick_broadcast or not (two functions). There > > is no need to check CPU feature on every entry. > > > > Hi, > > static_cpu_has() uses alternatives patching, so the cpu feature is not > tested on every entry. With the arat flag set you just have two nops > in the straight-line code path with this patch. > Thanks for explaining, i didn't know it was self modifying. Acked-by: Jacob Pan <jacob.jun.pan@linux.intel.com> ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2017-10-06 21:06 UTC | newest] Thread overview: 4+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- [not found] <bug-109051-18156@https.bugzilla.kernel.org/> 2017-10-06 17:19 ` [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT) Jason Baron 2017-10-06 18:36 ` Jacob Pan 2017-10-06 18:41 ` Jason Baron 2017-10-06 21:09 ` Jacob Pan
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