Re: [PATCH v4 5/5] clocksource: mips-gic-timer: Use local counter on synced multi-cluster systems

[Benoît Monin]

On Tuesday, 29 September 2026 at 18:59:16 CEST, Thomas Bogendoerfer wrote:
> >  static int gic_starting_cpu(unsigned int cpu)
> >  {
> > -      /* Ensure the GIC counter is running */
> > -      clear_gic_config(GIC_CONFIG_COUNTSTOP);
> > +      unsigned int cluster = cpu_cluster(&cpu_data[cpu]);
> > +
> > +      if (read_gic_config() & GIC_CONFIG_COUNTSTOP) {
> > +              clear_gic_config(GIC_CONFIG_COUNTSTOP);
> > +
> > +              if (cluster && mips_cm_is64 && !gic_clock_unstable)
> > +                      gic_sync_counter_64(cluster);
> > +
> > +              if (gic_synced_cl_map &&
> > +                  bitmap_full(gic_synced_cl_map, mips_cps_numclusters()))
> > +                      schedule_work(&gic_promote_work);
> 
> do we really need the workqueue ? As far as I understand
> sched_clock_register() doesn't use the clocksource mutex, so we should
> be able to directly call gic_promote() again.

With CONFIG_IRQ_TIME_ACCOUNTING=y, calling sched_clock_register() from the
CPU hotplug STARTING callback leads to a deadlock. We also need the
workqueue to call it.

Best regards,
-- 
Benoît Monin, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com