On Tue, Aug 25, 2020 at 03:41:48PM -0300, Marcelo Tosatti wrote: > When enabling per-CPU posix timers, an IPI to nohz_full CPUs might be > performed (to re-read the dependencies and possibly not re-enter > nohz_full on a given CPU). > > A common case is for applications that run on nohz_full= CPUs > to not use POSIX timers (eg DPDK). This patch skips the IPI > in case the task allowed mask does not intersect with nohz_full= CPU mask, > when going through tick_nohz_dep_set_signal. > > This reduces interruptions to nohz_full= CPUs. > > Signed-off-by: Marcelo Tosatti <[email protected]> [...] > /* > + * Set bit on nohz full dependency, kicking all cpus > + * only if task can run on nohz full CPUs. > + */ > +static void tick_nohz_dep_set_all_cond(struct task_struct *tsk, > + atomic_t *dep, > + enum tick_dep_bits bit) > +{ > + int prev; > + unsigned long flags; > + > + prev = atomic_fetch_or(BIT(bit), dep); > + if (prev) > + return; > + > + raw_spin_lock_irqsave(&tsk->pi_lock, flags); > + if (cpumask_intersects(&tsk->cpus_mask, tick_nohz_full_mask)) > + tick_nohz_full_kick_all();
So that's for one task but what about the other threads in that process? We are setting the tick dependency on all tasks sharing that struct signal. Thanks. > + raw_spin_unlock_irqrestore(&tsk->pi_lock, flags); > +} > +
