Re: [PATCH v2 2/6] arm64: perf: Implement correct cap_user_time

[Leo Yan]

Hi Peter,

On Wed, Jul 15, 2020 at 10:38:00AM +0200, Peter Zijlstra wrote:
> On Wed, Jul 15, 2020 at 10:05:08AM +0800, Leo Yan wrote:
> 
> > [leoyan: Use quot/rem to convert cyc to ns to avoid overflow]
> 
> > +		quot = rd->epoch_cyc >> rd->shift;
> > +		rem = rd->epoch_cyc & (((u64)1 << rd->shift) - 1);
> > +		ns = quot * rd->mult + ((rem * rd->mult) >> rd->shift);
> > +		userpg->time_zero -= ns;
> 
> I think we have mul_u64_u32_shr() for that.

Will fix it in next spin.

Thanks for suggestion,
Leo