oprofile and ARM A9 hardware counter

[Will Deacon]

On Fri, Jan 27, 2012 at 01:47:01PM +0000, Måns Rullgård wrote:
> Will Deacon <will.deacon at arm.com> writes:
> 
> > Mans,
> >
> > On Fri, Jan 27, 2012 at 12:56:35PM +0000, Måns Rullgård wrote:
> >> Will Deacon <will.deacon at arm.com> writes:
> >> > Did this lead anywhere in the end? It seems as though Ming Lei has a working
> >> > setup but Stephane is unable to replicate it, despite applying the necessary
> >> > patches and trying an updated bootloader.
> >> 
> >> With the patches listed above plus the one in [1], I get PMU interrupts.
> >> However, unless I restrict the profiled process to one CPU
> >> (taskset 1 perf record ...), I get a panic in armpmu_event_update() with
> >> the 'event' argument being null when called from armv7pmu_handle_irq().
> >> 
> >> [1] http://article.gmane.org/gmane.linux.ports.arm.omap/69696
> >
> > Great, thanks for trying this out. Which version of the kernel were you
> > using? I fixed a bunch of NULL pointer derefs. during the 3.2 window, but if
> > you were using an -rc kernel you have have hit one of them.
> 
> This was with the Linaro tilt-3.2 kernel from
> git://git.linaro.org/landing-teams/working/ti/kernel.git, commit
> 73e2c294444f209d281f7cd10b52b53b087e74f1.  Maybe one of the many patches
> it has on top of 3.2 is to blame.

Perhaps, or (more likely) the interrupt affinity for the CTI isn't working
properly and the interrupt is always delivered to CPU0. I'll keep this in
mind in case we get any more reports like this.

Cheers,

Will