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    SubjectRe: [PATCH 5/5] x86/intel_rdt: hotcpu updates for RDT


    On Wed, 1 Mar 2017, Thomas Gleixner wrote:

    >> WARN_ON(c->x86_cache_occ_scale != cqm_l3_scale);
    >>
    >> @@ -1585,12 +1580,17 @@ static int intel_cqm_cpu_starting(unsigned int cpu)
    >>
    >> static int intel_cqm_cpu_exit(unsigned int cpu)
    >> {
    >> + struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
    >
    > Can be this_cpu_ptr() because the callback is guaranteed to run on the
    > outgoing CPU.

    Will fix this. Assumed the calls are setup cache alloc way -
    cpuhp_setup_state(CPUHP_AP_ONLINE_DYN ..

    >
    >> int target;
    >>
    >> /* Is @cpu the current cqm reader for this package ? */
    >> if (!cpumask_test_and_clear_cpu(cpu, &cqm_cpumask))
    >> return 0;
    >
    > So if the CPU is not the current cqm reader then the per cpu state of this
    > CPU is left stale. Great improvement.
    >
    >> + state->rmid = 0;
    >> + state->rmid_usecnt = 0;
    >> + wrmsr(MSR_IA32_PQR_ASSOC, 0, state->closid);
    >
    > What clears state->closid? And what guarantees that state->rmid is not
    > updated before the CPU has really gone away?

    - The rdt code takes care of clearing closid state now. Will update the comment.
    - The cqm however was never writing a zero to PQR_ASSOC.

    So the update needs to be - to remove the state->closid = 0 from cqm code as the
    rdt code takes care of closid state in clear_closid() called from both offline and
    online cpu.
    And also write a rmid = 0 to PQR_ASSOC.

    We can integrate the two of these hot cpu calls(from cat and cqm) to write PQR
    only once.

    guess I can skip all of these and send it as part of cqm changes we planned
    anyways, because this is really a cqm change.

    Thanks,
    Vikas

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