linux-kernel - RE: [PATCH v11 01/13] x86/resctrl: Replace smp_call_function_many() with on_each_cpu

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Message-ID: <DS7PR11MB60772F09B9749307CFA0ED0DFCFF9@DS7PR11MB6077.namprd11.prod.outlook.com>
Date:   Tue, 10 Jan 2023 20:58:47 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Moger, Babu" <Babu.Moger@....com>,
        Ashok Raj <ashok_raj@...ux.intel.com>
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Subject: RE: [PATCH v11 01/13] x86/resctrl: Replace smp_call_function_many()
 with on_each_cpu_mask()

> > > + /* Update resource control msr on all the CPUs. */
> > > + on_each_cpu_mask(cpu_mask, rdt_ctrl_update, &msr_param, 1);
> >
> > Do you require these updates to done immediately via an IPI? or can they be
> > done bit lazy via schedule_on_each_cpu()?
>
> I have not experimented with lazy schedule.  At least I know the call
> update_cpu_closid_rmid should be completed immediately. Otherwise, the
> result might be inconsistent as the tasks(or CPUs)  could be running on
> two different closed/rmids before it is updated on all CPUs in the domain.

I think this does need to happen somewhat urgently. Imagine trying to give
some extra resources to a CPU bound real-time process. That process will
keep running with the old resource allocation.

-Tony