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Will Cohen writes: > Mikael Pettersson wrote: > > Philippe Elie writes: > > > From: Will Cohen <wcohen@redhat.com> > > > > > > Add oprofile support for Pentium Mobile (P6 core). Pentium Mobile needs > > > to unmask LVPTC vector, since it doesn't hurt other P6 core based cpus > > > we do it unconditionally for all these. > > > > [Patch talking about the Pentium-M.] > > > > I can find no support in Intel's documentation (IA32 Volume 3, > > 25366813.pdf) that Pentium-M:s need to unmask LVTPC. > > > > How certain are you of this? Is this an undocumented hardware > > quirk? If it is documented, please indicate where. > > I have tested it on a Pentium M machine. Without the unmask LVTPC the > nmi handler collected precisely one interrupt. With the LVTPC unmask the > OProfile data collection worked normally. > > > It's my theory that P4 added the auto-masking to help PEBS > > buffer overflow situations, but since P-M doesn't have PEBS, > > they shouldn't have had to change this on P-M as well. > > OTOH, it's certainly possible they changed it by accident. > > My theory is that the Pentium M uses same bus interface and local apic > as the Pentium M. Thus, the Pentium M shares the Pentium 4 need to > unmask LVTPC. Sounds reasonable and is consistent with other P-M vs P6 changes. > > One way of testing this would be to run a P-M with > > nmi_watchdog=2. If the NMI counter keeps ticking, then > > LVTPC does not need unmasking. > > Yes, I tested the nmi watchdog and it currently does not work on the > Pentium M. It doesn't get the later interrupts and states it is stuck. That confirms the "undocumented HW quirk" theory. Thanks. I'll fix the (in-kernel) NMI watchdog and (out-of-kernel) perfctr drivers. /Mikael - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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