So I spent the day cuddled up with my pdf of Intel Vol 3B, re-reading Chapter 18 with a hope of understanding i7. If any of the below is muddled or just plain wrong, I'd welcome clarification...
Looks to me like there's 3 fixed counters, just like the good ol' days, and 4 programmable counters with some restrictions on what can be counted where (some events are counter 0 only; some are counters 0 and 1 only). Everything's per *logical* (hyper-)thread unless and until the thread-any bit is implemented, and any counter (including fixed) can overflow. All 4 counters are PEBS enabled. And then there's the uncore. It has an additional 8 counters, and a bunch of interesting events. No restrictions on what can be counted where, but everything's system-wide. No clear indication of how contention between cores for these resources is resolved. I assume programming these things is atomic, but that doesn't resolve who 'owns' what. I suppose that could be done a'la' SiCortex, with each core getting 2 counters (but what about logical cores?). Probably a better way would be to let perfmon reserve resources on a first-come, first-served basis? I'm not sure that uncore counters should be restricted to system-wide counting only; I think it could be quite useful, as Phil described for SiCortex, to measure "what's happening to this shared resource while I'm active". That's not unlike Component PAPI measuring network activity on a NIC from within a first-person interface. Maybe the "oncore" events could be implemented as a traditional PAPI CPU interface and the "uncore" events could be implemented as a second PAPI component. That raises a question whether there can be two simultaneous perfmon sessions active at the same time (system-wide and first-person). Fun times; interesting questions... - dan > -----Original Message----- > From: Corey J Ashford [mailto:[EMAIL PROTECTED] > Sent: Friday, November 28, 2008 2:53 PM > To: Philip Mucci > Cc: [EMAIL PROTECTED]; perfmon2-devel > Subject: Re: [perfmon2] Intel Core i7 specs available. > > Philip Mucci <[EMAIL PROTECTED]> wrote on 11/28/2008 09:38:37 AM: > > > > I will release support for core and uncore. But uncore will be > > > restricted to system-wide sessions only. It does not make sense > > > to support this for per-thread session, as there is no correlation > > > possible with a PID or even a CPU. > > > > This is true only if you assume each process wants all of the 'off-core' > > > counters. > > > > An approach we took on SiCortex for our 'off-core' PMU, was to partition > > > the 256 counters into 6 blocks of 42, each process on each core gets 42 > > counters, dedicated. So there is no contention for these registers, and > > they can measure system-wide-events, but maintain the idea of a first > > person context, since, after all that is the workload that is being > > measured. When the process on that core is not active, neither is the > > perfmon context...so the counts are stopped. We can do very nice > > sampling on external events, DDR transactions, pciE stuff, fabric > > packets, using the same interface we do for the in-core counters, and > > these happen only when the process is active in non-system-wide mode. > > When you have two or more processes active, and one process (at least) is > sampling these off-core events on its dedicated counters, don't you still > end up with the same problem of getting events from other processes mixed > up with yours? I can see that it does give you a better idea about the > events while your process is running, because they are disabled while your > process is not running. > > - Corey > > Corey Ashford > Software Engineer > IBM Linux Technology Center, Linux Toolchain > Beaverton, OR > 503-578-3507 > [EMAIL PROTECTED] > > > > ------------------------------------------------------------------------- > This SF.Net email is sponsored by the Moblin Your Move Developer's > challenge > Build the coolest Linux based applications with Moblin SDK & win great > prizes > Grand prize is a trip for two to an Open Source event anywhere in the > world > http://moblin-contest.org/redirect.php?banner_id=100&url=/ > _______________________________________________ > perfmon2-devel mailing list > perfmon2-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/perfmon2-devel ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
