On Mon, May 11, 2015 at 09:43:41AM -0700, Stephane Eranian wrote: > On Mon, May 11, 2015 at 9:36 AM, Peter Zijlstra <[email protected]> wrote: > > On Mon, May 11, 2015 at 09:32:33AM -0700, Stephane Eranian wrote: > >> >> This is a minimal change. In principle the ACK could be moved much > >> >> later. > >> > > >> > Right, so the more complete change would be to use the new and improved > >> > FREEZE_ON_PMI and reenable both the LBRs and the CTRs with the > >> > STATUS_RESET MSR, right? > >> > > >> > Does it make sense to have a new handle_irq() routine for that? > >> > >> Were we not already using FREEZE_ON_PMI with LBR (except for one > >> erratum on HSW)? > > > > That's FREEZE_LBRS_ON_PMI, I was referring to FREEZE_PERFMON_ON_PMI, > > which we've not used so far. > > > Ah, yes that one was not used so far. I don't quite remember why. > I think with PEBS, you don't need it or it should be off or something like > this.
The LBR freeze should work with call stack mode if you use PEBS events. So in theory we could allow call-stack lbr for kernel with such a restriction. But we have a working kernel backtrace anyways, so it's not really critical. > > > I think Andi tried using it before, but there's some issues with it on > > v3, but v4 should have fixed all that. > > > I was referring to a LBR issue on v3 (HSW) and call stack mode. > > > Andi can you perhaps explain what the problem with FREEZE_PERFMON_ON_PMI > > on v3 was again? I'm not sure why we never used it. The update of the DEBUGCTL can race with other operations, but it's rather obscure. But I would not do it right now. -Andi -- [email protected] -- Speaking for myself only -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
