Messages in this thread | | | Subject | Re: [PATCH 5/7] perf: Optimise topology iteration | From | Lin Ming <> | Date | Tue, 04 Jan 2011 15:13:02 +0800 |
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On Mon, 2011-01-03 at 23:20 +0800, Andi Kleen wrote: > On Mon, Jan 03, 2011 at 12:02:10PM +0100, Peter Zijlstra wrote: > > On Mon, 2010-12-27 at 23:38 +0800, Lin Ming wrote: > > > Currently we iterate the full machine looking for a matching core_id/nb > > > for the percore and the amd northbridge stuff , using a smaller topology > > > mask makes sense. > > > > Does topology_thread_cpumask() include offline cpus? I tried looking at > > it, but I cannot find any code clearing bits in that mask on offline. > > The problem is not only at offline, but also at online between CPUs > going online. I don't think the patch is a good idea and it doesn't
I didn't see the problem.
Assume logical cpu 3, 7 are 2 threads in a core, and they are plug/unpluged as below sequence, CPU 3 offline, CPU7 offline, CPU3 online, CPU7 online
1. After cpu3 offline
topology_thread_cpumask(3) returns empty topology_thread_cpumask(7) returns 7
2. After CPU7 offline
topology_thread_cpumask(3) returns empty topology_thread_cpumask(7) returns empty
3. When CPU3 online, calling intel_pmu_cpu_starting
topology_thread_cpumask(3) returns 3 topology_thread_cpumask(7) returns empty
for_each_cpu(i, topology_thread_cpumask(cpu)) { struct intel_percore *pc = per_cpu(cpu_hw_events, i).per_core;
if (pc && pc->core_id == core_id) { kfree(cpuc->per_core); cpuc->per_core = pc; break; } }
Above "if" statement will not be executed, because pc->core_id was initialized to -1 in intel_pmu_cpu_prepare.
4. When CPU7 online, calling intel_pmu_cpu_starting
topology_thread_cpumask(3) returns 3, 7 topology_thread_cpumask(7) returns 3, 7
for_each_cpu(i, topology_thread_cpumask(cpu)) { struct intel_percore *pc = per_cpu(cpu_hw_events, i).per_core;
if (pc && pc->core_id == core_id) { kfree(cpuc->per_core); cpuc->per_core = pc; break; } }
cpuc->per_core->core_id = core_id; cpuc->per_core->refcnt++;
Above "if" statement will be executed and the per_core data allocated for cpu7 will be freed.
All above is right, or could you explain more about the problem at CPUs offline and online?
Thanks, Lin Ming
> even have any advantages either since this is a initialization only > slow path. > > -Andi
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