| Message ID | 20191202164506.28845-1-l.stach@pengutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm/twd: avoid waking deeply sleeping CPUs for rate change notifier | expand |
On 02/12/2019 17:45, Lucas Stach wrote: > The current clock notifier sends an IPI to all CPUs, even if they are in > deep sleep state with the local timer disabled and switched to tick > broadcast. This needlessly cuts the CPU sleep times, as nothing is gained > from updating a disabled TWDs rate. > > Keep track of the enabled TWDs and only send an IPI to those CPUs with an > active local timer. As disabled TWDs may now miss a CPU frequency update > we need to make sure to refresh the rate on re-enabling of the timer. Sounds like a nice optimization. However I'm not sure about the solidity of the solution regarding the existing. The twd_update_frequency() function is called in parallel on each cpu and they all change the global variable twd_timer_rate. The proposed solution relies on the existing mechanism where we can be calling clockevents_update_freq() while twd_update_frequency() is called on another CPU. In addition, the frequency update may be needed in other drivers, like the mips-gic-timer.c. May be a generic solution would be appropriate. > Signed-off-by: Lucas Stach <l.stach@pengutronix.de> > --- > arch/arm/kernel/smp_twd.c | 31 +++++++++++++++++++++++++++++-- > 1 file changed, 29 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c > index 9a14f721a2b0..3055c2623d4d 100644 > --- a/arch/arm/kernel/smp_twd.c > +++ b/arch/arm/kernel/smp_twd.c > @@ -29,6 +29,8 @@ static struct clk *twd_clk; > static unsigned long twd_timer_rate; > static DEFINE_PER_CPU(bool, percpu_setup_called); > > +static cpumask_var_t active_twd_mask; > + > static struct clock_event_device __percpu *twd_evt; > static unsigned int twd_features = > CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT; > @@ -36,12 +38,24 @@ static int twd_ppi; > > static int twd_shutdown(struct clock_event_device *clk) > { > + cpumask_clear_cpu(smp_processor_id(), active_twd_mask); > + > writel_relaxed(0, twd_base + TWD_TIMER_CONTROL); > return 0; > } > > static int twd_set_oneshot(struct clock_event_device *clk) > { > + cpumask_set_cpu(smp_processor_id(), active_twd_mask); > + > + /* > + * When going from shutdown to oneshot we might have missed some > + * frequency updates if the CPU was sleeping. Make sure to update > + * the timer frequency with the current rate. > + */ > + if (clockevent_state_shutdown(clk)) > + clockevents_update_freq(clk, twd_timer_rate); > + > /* period set, and timer enabled in 'next_event' hook */ > writel_relaxed(TWD_TIMER_CONTROL_IT_ENABLE | TWD_TIMER_CONTROL_ONESHOT, > twd_base + TWD_TIMER_CONTROL); > @@ -54,6 +68,16 @@ static int twd_set_periodic(struct clock_event_device *clk) > TWD_TIMER_CONTROL_IT_ENABLE | > TWD_TIMER_CONTROL_PERIODIC; > > + cpumask_set_cpu(smp_processor_id(), active_twd_mask); > + > + /* > + * When going from shutdown to periodic we might have missed some > + * frequency updates if the CPU was sleeping. Make sure to update > + * the timer frequency with the current rate. > + */ > + if (clockevent_state_shutdown(clk)) > + clockevents_update_freq(clk, twd_timer_rate); > + > writel_relaxed(DIV_ROUND_CLOSEST(twd_timer_rate, HZ), > twd_base + TWD_TIMER_LOAD); > writel_relaxed(ctrl, twd_base + TWD_TIMER_CONTROL); > @@ -119,8 +143,8 @@ static int twd_rate_change(struct notifier_block *nb, > * changing cpu. > */ > if (flags == POST_RATE_CHANGE) > - on_each_cpu(twd_update_frequency, > - (void *)&cnd->new_rate, 1); > + on_each_cpu_mask(active_twd_mask, twd_update_frequency, > + (void *)&cnd->new_rate, 1); > > return NOTIFY_OK; > } > @@ -273,6 +297,9 @@ static int __init twd_local_timer_common_register(struct device_node *np) > { > int err; > > + if (!zalloc_cpumask_var(&active_twd_mask, GFP_KERNEL)) > + return -ENOMEM; > + > twd_evt = alloc_percpu(struct clock_event_device); > if (!twd_evt) { > err = -ENOMEM; >
diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c index 9a14f721a2b0..3055c2623d4d 100644 --- a/arch/arm/kernel/smp_twd.c +++ b/arch/arm/kernel/smp_twd.c @@ -29,6 +29,8 @@ static struct clk *twd_clk; static unsigned long twd_timer_rate; static DEFINE_PER_CPU(bool, percpu_setup_called); +static cpumask_var_t active_twd_mask; + static struct clock_event_device __percpu *twd_evt; static unsigned int twd_features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT; @@ -36,12 +38,24 @@ static int twd_ppi; static int twd_shutdown(struct clock_event_device *clk) { + cpumask_clear_cpu(smp_processor_id(), active_twd_mask); + writel_relaxed(0, twd_base + TWD_TIMER_CONTROL); return 0; } static int twd_set_oneshot(struct clock_event_device *clk) { + cpumask_set_cpu(smp_processor_id(), active_twd_mask); + + /* + * When going from shutdown to oneshot we might have missed some + * frequency updates if the CPU was sleeping. Make sure to update + * the timer frequency with the current rate. + */ + if (clockevent_state_shutdown(clk)) + clockevents_update_freq(clk, twd_timer_rate); + /* period set, and timer enabled in 'next_event' hook */ writel_relaxed(TWD_TIMER_CONTROL_IT_ENABLE | TWD_TIMER_CONTROL_ONESHOT, twd_base + TWD_TIMER_CONTROL); @@ -54,6 +68,16 @@ static int twd_set_periodic(struct clock_event_device *clk) TWD_TIMER_CONTROL_IT_ENABLE | TWD_TIMER_CONTROL_PERIODIC; + cpumask_set_cpu(smp_processor_id(), active_twd_mask); + + /* + * When going from shutdown to periodic we might have missed some + * frequency updates if the CPU was sleeping. Make sure to update + * the timer frequency with the current rate. + */ + if (clockevent_state_shutdown(clk)) + clockevents_update_freq(clk, twd_timer_rate); + writel_relaxed(DIV_ROUND_CLOSEST(twd_timer_rate, HZ), twd_base + TWD_TIMER_LOAD); writel_relaxed(ctrl, twd_base + TWD_TIMER_CONTROL); @@ -119,8 +143,8 @@ static int twd_rate_change(struct notifier_block *nb, * changing cpu. */ if (flags == POST_RATE_CHANGE) - on_each_cpu(twd_update_frequency, - (void *)&cnd->new_rate, 1); + on_each_cpu_mask(active_twd_mask, twd_update_frequency, + (void *)&cnd->new_rate, 1); return NOTIFY_OK; } @@ -273,6 +297,9 @@ static int __init twd_local_timer_common_register(struct device_node *np) { int err; + if (!zalloc_cpumask_var(&active_twd_mask, GFP_KERNEL)) + return -ENOMEM; + twd_evt = alloc_percpu(struct clock_event_device); if (!twd_evt) { err = -ENOMEM;
The current clock notifier sends an IPI to all CPUs, even if they are in deep sleep state with the local timer disabled and switched to tick broadcast. This needlessly cuts the CPU sleep times, as nothing is gained from updating a disabled TWDs rate. Keep track of the enabled TWDs and only send an IPI to those CPUs with an active local timer. As disabled TWDs may now miss a CPU frequency update we need to make sure to refresh the rate on re-enabling of the timer. Signed-off-by: Lucas Stach <l.stach@pengutronix.de> --- arch/arm/kernel/smp_twd.c | 31 +++++++++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-)