Messages in this thread | | | Date | Mon, 25 Apr 2011 15:12:58 -0700 | From | Andi Kleen <> | Subject | Re: [PATCH 1/1] perf tools: Add missing user space support for config1/config2 |
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> The PAPI tool was using the perf_events interface in the 2.6.39-git > kernels to collect offcore response results by properly setting the > config1 register on Nehalem and Westmere machines.
I already had some users for this functionality too. Offcore events are quite useful for various analysis: basically every time you have a memory performance problem -- especially a NUMA problem -- they can help you a lot tracking it down.
They answer questions like "who accesses memory on another node"
As far as I'm concerned b52c55c6a25e4515b5e075a989ff346fc251ed09 is a bad feature regression.
> > Now it has been disabled for unclear reasons.
Also unfortunately only partial. Previously you could at least write the MSR from user space through /dev/cpu/*/msr, but now the kernel randomly rewrites it if anyone else uses cache events.
Right now I have some frontend scripts which are doing this, but it's really quite nasty.
It's very sad we have to go through this.
-Andi
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