RE: [PATCH 1/3] perf/x86: add sysfs entry to freeze counter on SMI

[Liang, Kan]

> On Thu, Mar 23, 2017 at 11:25:49AM -0700, kan.liang@xxxxxxxxx wrote:
> > From: Kan Liang <Kan.liang@xxxxxxxxx>
> >
> > When setting FREEZE_WHILE_SMM bit in IA32_DEBUGCTL, all
> performance
> > counters will be effected. There is no way to do per-counter freeze on
> > smi. So it should not use the per-event interface (e.g. ioctl or event
> > attribute) to set FREEZE_WHILE_SMM bit.
> >
> > Adds sysfs entry /sys/device/cpu/freeze_on_smi to set
> FREEZE_WHILE_SMM
> > bit in IA32_DEBUGCTL. When set, freezes perfmon and trace messages
> > while in SMM.
> > Value has to be 0 or 1. It will be applied to all possible cpus.
> 
> So is there ever a good reason to not set this?

For me, I don't see any drawbacks to set it unconditionally.
But I'm not sure if there is someone else who may want the counter
running in SMI.

If there is no objection, I will set the FREEZE_WHILE_SMM bit
unconditionally in next version.

Thanks,
Kan