linux-kernel - Re: [PATCH v5 6/7] powerpc/powernv: generic nest pmu event functions

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Date:	Thu, 23 Jul 2015 19:04:19 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
Cc:	Daniel Axtens <dja@...ens.net>, linux-kernel@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org,
	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 6/7] powerpc/powernv: generic nest pmu event functions

On Thu, 2015-07-23 at 12:14 +0530, Madhavan Srinivasan wrote:
> 
> On Wednesday 22 July 2015 10:26 AM, Daniel Axtens wrote:
> >> +static void p8_nest_read_counter(struct perf_event *event)
> >> +{
> >> +	uint64_t *addr;
> >> +	u64 data = 0;
> > You've got a u64 and a uint64_t, and then...
> >> +
> >> +	addr = (u64 *)event->hw.event_base;
> > ... you cast to event_base to a u64 pointer, which you assign to a
> > uint64_t pointer.
> >> +	data = __be64_to_cpu(*addr);
> > And now you dereference the pointer.
> > Could you just have:
> >     data = __be64_to_cpu(*event->hw.event_base);
> >> +	local64_set(&event->hw.prev_count, data);
> >> +}
> >> +
> >> +static void p8_nest_perf_event_update(struct perf_event *event)
> >> +{
> >> +	u64 counter_prev, counter_new, final_count;
> >> +	uint64_t *addr;
> >> +
> >> +	addr = (uint64_t *)event->hw.event_base;
> > Here at least the cast type is the same as the type of addr, but again,
> > why do you need the different types, and why local variable?
> 
> Damn sorry, copy paste errors. When I added debug prints i messed
> the type case in both the functions. I will make them as uint64_t.

No please use u64/u32 etc. Most code in powerpc does and I prefer them.

cheers


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