Re: [perfmon2] II.1 - Fixed counters on Intel
Status: Beta
Brought to you by:
seranian
From: Ingo M. <mi...@el...> - 2009-06-22 11:57:27
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> II/ X86 comments > > 1/ Fixed counters on Intel > > You cannot simply fall back to generic counters if you cannot find > a fixed counter. There are model-specific bugs, for instance > UNHALTED_REFERENCE_CYCLES (0x013c), does not measure the same > thing on Nehalem when it is used in fixed counter 2 or a generic > counter. The same is true on Core. This could be handled via a model specific quirk, if the erratum is serious enough. > You cannot simply look at the event field code to determine > whether this is an event supported by a fixed counters. You must > look at the other fields such as edge, invert, cnt-mask. If those > are present then you have to fall back to using a generic counter > as fixed counters only support priv level filtering. As indicated > above, though, programming UNHALTED_REFERENCE_CYCLES on a generic > counter does not count the same thing, therefore you need to fail > if filters other than priv levels are present on this event. Agreed, we'll fix this. |