On 2023-03-15 17:49:10 [+0100], Krzysztof Kozlowski wrote: > Qualcomm cpufreq driver configures interrupts with affinity to each > cluster, e.g. dcvsh-irq-0, dcvsh-irq-4 and dcvsh-irq-7 on SM8250. > Triggered interrupt will schedule delayed work, but, since workqueue > prefers local CPUs, it might get executed on a CPU dedicated to realtime > tasks causing unexpected latencies in realtime workload. > > Use unbound workqueue for such case. This might come with performance > or energy penalty, e.g. because of cache miss or when other CPU is > sleeping. I miss the point where it explains that only PREEMPT_RT is affected by this. > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> > --- > drivers/cpufreq/qcom-cpufreq-hw.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c > index 2f581d2d617d..c5ff8d25fabb 100644 > --- a/drivers/cpufreq/qcom-cpufreq-hw.c > +++ b/drivers/cpufreq/qcom-cpufreq-hw.c > @@ -390,7 +390,16 @@ static irqreturn_t qcom_lmh_dcvs_handle_irq(int irq, void *data) > > /* Disable interrupt and enable polling */ > disable_irq_nosync(c_data->throttle_irq); > - schedule_delayed_work(&c_data->throttle_work, 0); > + > + /* > + * Workqueue prefers local CPUs and since interrupts have set affinity, > + * the work might execute on a CPU dedicated to realtime tasks. > + */ > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) > + queue_delayed_work_on(WORK_CPU_UNBOUND, system_unbound_wq, > + &c_data->throttle_work, 0); > + else > + schedule_delayed_work(&c_data->throttle_work, 0); You isolated CPUs and use this on PREEMPT_RT. And this special use-case is your reasoning to make this change and let it depend on PREEMPT_RT? If you do PREEMPT_RT and you care about latency I would argue that you either disable cpufreq and set it to PERFORMANCE so that the highest available frequency is set once and not changed afterwards. > if (qcom_cpufreq.soc_data->reg_intr_clr) > writel_relaxed(GT_IRQ_STATUS, > -- > 2.34.1 >
