arm64 sched_clock cpu accounting

[will.deacon@arm.com (Will Deacon)]

On Wed, Dec 02, 2015 at 03:42:10PM -0800, Mario Smarduch wrote:
> On 12/2/2015 10:07 AM, Christoffer Dall wrote:
> > On Wed, Nov 18, 2015 at 06:20:03PM -0800, Mario Smarduch wrote:
> >> Also with tick accounting enabled, and periodic timer HZ set to 1000 no irq time
> >> is reported. That's with running a ping flood - 1200 int/s, not sure why
> >> wouldn't any irq time be reported? The other two modes report irq time as expected.
> >>
> >> On 11/18/2015 11:46 AM, Mario Smarduch wrote:
> >>> Hello,
> >>>   I noticed sched clock accounting can be enabled when arch-timer is
> >>> initialized. But arm64 doesn't appear to have 'HAVE_IRQ_TIME_ACCOUNTING'
> >>> selected (as of mainline 4.4-rc1) and IRQ_TIME_ACCOUNTING can't be selected.
> >>> After adding it to arch/arm64/Kconfig, option appears to work fine. Depending on
> >>> need all accounting options are fine, but irq time accounting appears to be most
> >>> preferable.
> >>>
> >>> Any thoughts? Is it fine to enable it?
> >>>
> > Is any of this related to KVM?
> 
> Indirectly, given the guest should yield same results. To be on the safe side I
> ran the guest in all combinations (7) to confirm that's the case.
> 
> Also verified that guest time on host appears fine in all these configurations.
> It takes extra effort to get the guest time as opposed to other modes.

I can take this via the arm64 tree (where it's queued, but I've not pushed
anything yet).

Will