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

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Date:	Wed, 22 Jul 2015 14:56:01 +1000
From:	Daniel Axtens <dja@...ens.net>
To:	Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
Cc:	linuxppc-dev@...ts.ozlabs.org, 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>,
	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 6/7] powerpc/powernv: generic nest pmu event functions


> +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?
> +	counter_prev = local64_read(&event->hw.prev_count);
> +	counter_new = __be64_to_cpu(*addr);
> +	final_count = counter_new - counter_prev;
> +
> +	local64_set(&event->hw.prev_count, counter_new);
> +	local64_add(final_count, &event->count);
> +}
> +
> +static void p8_nest_event_start(struct perf_event *event, int flags)
> +{
> +	event->hw.state = 0;
Should this be an enum or a #define rather than a bare 0? (It may not
need to be, I was just wondering because I don't know what 0 means.)
> +	p8_nest_read_counter(event);
> +}
> +
-- 
Regards,
Daniel

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