Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Thu, 20 Jan 2022 19:55:57 +0100 | Subject | Re: [PATCH] cpuidle: menu: Fix long delay issue when tick stopped |
| |
On Mon, Jan 17, 2022 at 9:16 AM Shaokun Zhang <zhangshaokun@hisilicon.com> wrote: > > From: Guo Yang <guoyang2@huawei.com> > > The network delay was always big on arm server tested by qperf, > the reason was that the cpu entered deep power down idle state(like intel > C6) and can't goto a shallow one. > > The intervals in @get_typical_interval() was much smaller than predicted_ns > in @menu_select(), so the predict state is always deepest and cause long > time network delay. > > Every time when the cpu got an interrupt from the network, the cpu was > waken up and did the IRQ, after that the cpu enter @menu_select() > but the @tick_nohz_tick_stopped() was true and get a big data->next_timer_ns, > the cpu can never goto a shallow state util the data->next_timer_ns timeout. > Below was the print when the issue occurrence. > > [ 37.082861] intervals = 36us > [ 37.082875] intervals = 15us > [ 37.082888] intervals = 22us > [ 37.082902] intervals = 35us > [ 37.082915] intervals = 34us > [ 37.082929] intervals = 39us > [ 37.082942] intervals = 39us > [ 37.082956] intervals = 35us > [ 37.082970] target_residency_ns = 10000, predicted_ns = 35832710 > [ 37.082998] target_residency_ns = 600000, predicted_ns = 35832710 > [ 37.083037] intervals = 36us > [ 37.083050] intervals = 15us > [ 37.083064] intervals = 22us > [ 37.083077] intervals = 35us > [ 37.083091] intervals = 34us > [ 37.083104] intervals = 39us > [ 37.083118] intervals = 39us > [ 37.083131] intervals = 35us > [ 37.083145] target_residency_ns = 10000, predicted_ns = 35657420 > [ 37.083174] target_residency_ns = 600000, predicted_ns = 35657420 > [ 37.083212] intervals = 36us > [ 37.083225] intervals = 15us > [ 37.083239] intervals = 22us > [ 37.083253] intervals = 35us > [ 37.083266] intervals = 34us > [ 37.083279] intervals = 39us > [ 37.083293] intervals = 39us > [ 37.083307] intervals = 35us > [ 37.083320] target_residency_ns = 10000, predicted_ns = 35482140 > [ 37.083349] target_residency_ns = 600000, predicted_ns = 35482140 > > Add idle tick wakeup judge before change predicted_ns. > > Cc: "Rafael J. Wysocki" <rafael@kernel.org> > Cc: Daniel Lezcano <daniel.lezcano@linaro.org> > Signed-off-by: Guo Yang <guoyang2@huawei.com> > Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com> > --- > drivers/cpuidle/governors/menu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c > index c492268..3f03843 100644 > --- a/drivers/cpuidle/governors/menu.c > +++ b/drivers/cpuidle/governors/menu.c > @@ -313,7 +313,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, > get_typical_interval(data, predicted_us)) * > NSEC_PER_USEC; > > - if (tick_nohz_tick_stopped()) { > + if (tick_nohz_tick_stopped() && data->tick_wakeup) {
data->tick_wakeup is only true if tick_nohz_idle_got_tick() has returned true, but I'm not sure how this can happen after stopping the tick.
IOW, it looks like the change simply makes the condition be always false.
> /* > * If the tick is already stopped, the cost of possible short > * idle duration misprediction is much higher, because the CPU > -- > 1.8.3.1 >
| |