Re: [PATCH] perf/x86/amd/power: Use div64_u64 onstead of do_div()

[Jules Bashizi Irenge <jbi.octave@gmail.com>]

On Thu, May 02, 2024 at 04:25:58PM +0000, David Laight wrote:
> From: Jules Irenge <jbi.octave@gmail.com>
> > Sent: 28 April 2024 17:40
> > 
> > do_div() truncates a u64 divisor to 32 bit.
> > This can lead to non-zero being truncated to zero for division.
> > 
> > Fix coccinelle warning
> > WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead
> > 
> > Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
> > ---
> >  arch/x86/events/amd/power.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/events/amd/power.c b/arch/x86/events/amd/power.c
> > index 37d5b380516e..ff003c1a645b 100644
> > --- a/arch/x86/events/amd/power.c
> > +++ b/arch/x86/events/amd/power.c
> > @@ -64,7 +64,7 @@ static void event_update(struct perf_event *event)
> >  	delta *= cpu_pwr_sample_ratio * 1000;
> >  	tdelta = new_ptsc - prev_ptsc;
> > 
> > -	do_div(delta, tdelta);
> > +	div64_u64(delta, tdelta);
> 
> Nak - you've not tested it.
> 
> 	David
> 
No, I later realised it's for 32bit here. It may be very expensive for
a 32bit.
I think I got it wrong here.

Thanks for reply.
Jules