Re: [PATCH v1 2/9]powerpc/powernv: nest pmu init function with cpumask attr

[Madhavan Srinivasan]

On Wednesday 03 June 2015 04:44 AM, Daniel Axtens wrote:
> On Tue, 2015-06-02 at 21:29 +0530, Madhavan Srinivasan wrote:
> > Patch creates a file "nest-pmu-c" to contain nest pmu related functions.
> "nest-pmu.c"
> > Patch adds nest pmu init function and cpumask function since Nest pmu units
> > are per-chip. First online cpu for a given node is picked as
> > designated thread to read the counter data.
> >
> > Subsequent patch adds the hotplug support.
> >
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Paul Mackerras <paulus@xxxxxxxxx>
> > Cc: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> > Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
> > Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> > Cc: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Signed-off-by: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
> > ---
> >   arch/powerpc/perf/nest-pmu.c | 70 ++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 70 insertions(+)
> >   create mode 100644 arch/powerpc/perf/nest-pmu.c
> >
> > diff --git a/arch/powerpc/perf/nest-pmu.c b/arch/powerpc/perf/nest-pmu.c
> > new file mode 100644
> > index 0000000..d4413bb
> > --- /dev/null
> > +++ b/arch/powerpc/perf/nest-pmu.c
> > @@ -0,0 +1,70 @@
> > +/*
> > + * Nest Performance Monitor counter support for POWER8 processors.
> > + *
> > + * Copyright 2015 Madhavan Srinivasan, IBM Corporation.
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU General Public License
> > + * as published by the Free Software Foundation; either version
> > + * 2 of the License, or (at your option) any later version.
> > + */
> > +
> Again, I think this is supposed to be v2 only.
>
> > +#include "nest-pmu.h"
> > +
> > +static cpumask_t cpu_mask_nest_pmu;
> > +
> > +static ssize_t cpumask_nest_pmu_get_attr(struct device *dev,
> > +				struct device_attribute *attr, char *buf)
> > +{
> > +	return cpumap_print_to_pagebuf(true, buf, &cpu_mask_nest_pmu);
> > +}
> > +
> > +static DEVICE_ATTR(cpumask, S_IRUGO, cpumask_nest_pmu_get_attr, NULL);
> > +
> > +static struct attribute *cpumask_nest_pmu_attrs[] = {
> > +	&dev_attr_cpumask.attr,
> > +	NULL,
> > +};
> > +
> > +static struct attribute_group cpumask_nest_pmu_attr_group = {
> > +	.attrs = cpumask_nest_pmu_attrs,
> > +};
> > +
> > +void cpumask_chip(void)
> > +{
> > +	const struct cpumask *l_cpumask;
> > +	int cpu, nid;
> > +
> > +	if (!cpumask_empty(&cpu_mask_nest_pmu)) {
> > +		printk(KERN_INFO "cpumask not empty\n");
> > +		return;
> > + 	}
> > +
> > +	cpu_notifier_register_begin();
> > +	for_each_online_node(nid) {
> > +		l_cpumask = cpumask_of_node(nid);
> > +		cpu = cpumask_first(l_cpumask);
> > +		cpumask_set_cpu(cpu, &cpu_mask_nest_pmu);
> > +	}
> > +
> > +	cpu_notifier_register_done();
> > +}
> It's not clear from the name of this function what it does. I don't
> think I actually understand what it does: it appears to register a
> notifier on the first cpu of each node; maybe that should be reflected
> in the name.

My bad. Hotplug notification registration happens in the next patch.
could merge both as single patch.

> > +static int __init nest_pmu_init(void)
> > +{
> > +	int ret = 0;
> > +
> > +	/*
> > +	 * Lets do this only if we are hypervisor
> > +	 */
> > +	if (!cur_cpu_spec->oprofile_cpu_type ||
> > +	   strcmp(cur_cpu_spec->oprofile_cpu_type, "ppc64/power8") ||
> > +	   !cpu_has_feature(CPU_FTR_HVMODE))
> > +		return ret;
> > +
> > +	cpumask_chip();
> > +
> > +	return 0;
> > +}
>   - Where is ret set? I can only see it set when it's defined: the if
> statment doesn't change the value of ret as far as I can see...
Yes. It should have set to error value. Will fix it.

>   - Would it be clearer if you said
>          !(strcmp(cur_cpu_spec->oprofile_cpu_type, "ppc64/power8") == 0)
>     That would make it clearer that you're trying to get a list of
> possible failure conditions.
>   
Yes. Sure will change it.

>   - Is there really no better way to check if a CPU is a power 8 than an
> string comparison?
One other way I can think of is using PVR (Processor Version Register), 
but then will end up having multiple checks for Power8 itself, so this 
is lot simpler.

> > +device_initcall(nest_pmu_init);
> Regards,
> Daniel Axtens
Thanks for the review
Maddy

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