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

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Date:	Thu, 23 Jul 2015 12:14:28 +0530
From:	Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
To:	Daniel Axtens <dja@...ens.net>
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



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.

Thanks for this detail review
Maddy

>> +	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.)

I could remove it since was just initializing at the start.

>> +	p8_nest_read_counter(event);
>> +}
>> +

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