On Wed, Sep 02, 2020 at 01:38:59AM +0200, Frederic Weisbecker wrote:
> 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 <mtosa...@redhat.com>
> [...]
> > /*
> > + * 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.
Hi Frederic,
Yep, fixing in -v2, thanks.
