linux-kernel - Re: [PATCH v1 4/9]powerpc/powernv: Add generic nest pmu ops

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Date:	Thu, 04 Jun 2015 14:36:04 +0530
From:	Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
To:	Daniel Axtens <dja@...ens.net>
CC:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Stephane Eranian <eranian@...gle.com>,
	Paul Mackerras <paulus@...ba.org>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Subject: Re: [PATCH v1 4/9]powerpc/powernv: Add generic nest pmu ops



On Wednesday 03 June 2015 05:33 AM, Daniel Axtens wrote:
> On Tue, 2015-06-02 at 21:29 +0530, Madhavan Srinivasan wrote:
>> Patch adds generic nest pmu functions and format attribute.
>>
> I'm not sure this commit message accurately reflects the content of the
> patch. At any rate, please could you:
>   - say what the patch adds the functions and attributes to.
>   - phrase your message as "Add generic ..." not "Patch adds
> generic ...": see
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/SubmittingPatches#n155

Sure. Will rephrase it.
>
>>   
>> +PMU_FORMAT_ATTR(event, "config:0-20");
>> +struct attribute *p8_nest_format_attrs[] = {
>> +	&format_attr_event.attr,
>> +	NULL,
>> +};
>> +
>> +struct attribute_group p8_nest_format_group = {
>> +	.name = "format",
>> +	.attrs = p8_nest_format_attrs,
>> +};
> Can these structs be constified?
I guess it can. Will check it out.

>> +
>> +int p8_nest_event_init(struct perf_event *event)
>> +{
>> +	int chip_id;
>> +
>> +	if (event->attr.type != event->pmu->type)
>> +		return -ENOENT;
>> +
>> +	/* Sampling not supported yet */
>> +	if (event->hw.sample_period)
>> +		return -EINVAL;
>> +
>> +	/* unsupported modes and filters */
>> +	if (event->attr.exclude_user   ||
>> +	    event->attr.exclude_kernel ||
>> +	    event->attr.exclude_hv     ||
>> +	    event->attr.exclude_idle   ||
>> +	    event->attr.exclude_host   ||
>> +	    event->attr.exclude_guest  ||
>> +	    event->attr.sample_period) /* no sampling */
>> +		return -EINVAL;
> You test for sample period twice here.
Yes right. I will remove it.

>> +
>> +	if (event->cpu < 0)
>> +		return -EINVAL;
>> +
>> +	chip_id = topology_physical_package_id(event->cpu);
>> +	event->hw.event_base = event->attr.config +
>> +				p8_perchip_nest_info[chip_id].vbase;
>> +
>> +	return 0;
>> +}
>> +
>> +void p8_nest_read_counter(struct perf_event *event)
>> +{
>> +	u64 *addr;
>> +	u64 data = 0;
>> +
>> +	addr = (u64 *)event->hw.event_base;
>> +	data = __be64_to_cpu((uint64_t)*addr);
>> +	local64_set(&event->hw.prev_count, data);
>> +}
>> +
>> +void p8_nest_perf_event_update(struct perf_event *event)
>> +{
>> +	u64 counter_prev, counter_new, final_count;
>> +	uint64_t *addr;
>> +
>> +	addr = (u64 *)event->hw.event_base;
>> +	counter_prev = local64_read(&event->hw.prev_count);
>> +	counter_new = __be64_to_cpu((uint64_t)*addr);
>> +	final_count = counter_new - counter_prev;
>> +
>> +	local64_set(&event->hw.prev_count, counter_new);
>> +	local64_add(final_count, &event->count);
>> +}
>> +
>> +void p8_nest_event_start(struct perf_event *event, int flags)
>> +{
>> +	event->hw.state = 0;
>> +	p8_nest_read_counter(event);
>> +}
>> +
>> +void p8_nest_event_stop(struct perf_event *event, int flags)
>> +{
>> +	p8_nest_perf_event_update(event);
>> +}
>> +
>> +int p8_nest_event_add(struct perf_event *event, int flags)
>> +{
>> +	p8_nest_event_start(event, flags);
>> +	return 0;
>> +}
>> +
>> +void p8_nest_event_del(struct perf_event *event, int flags)
>> +{
>> +	p8_nest_event_stop(event, flags);
> Is this necessary?
>
> Stop calls update, which I guess makes sense as it finalises the value.
> But if the event is being deleted anyway, why not just do nothing here?
Since these Nest PMUs does not support sampling. IIUC, "perf record" 
interface uses
the event start/stop ops. Incase of perf stat interface event add/del 
interface are used to enable and disable the counters. Now, when we 
disable or delete, we update the event counter with the delta value.

>> +}
>> +
> Regards,
> Daniel Axtens

Thanks for the review
Maddy

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