Re: [PATCH] arm64: perf: Simplify the ARMv8 PMUv3 event attributes

From: Mark Rutland <mark.rutland@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: perf: Simplify the ARMv8 PMUv3 event attributes
Date: Fri, 1 Nov 2019 08:53:19 +0000	[thread overview]
Message-ID: <20191101085319.GA3508@blommer> (raw)
In-Reply-To: <20191031160804.GA28325@willie-the-truck>

On Thu, Oct 31, 2019 at 04:08:04PM +0000, Will Deacon wrote:
> On Wed, Oct 30, 2019 at 11:46:17AM +0800, Shaokun Zhang wrote:
> > For each PMU event, there is a ARMV8_EVENT_ATTR(xx, XX) and
> > &armv8_event_attr_xx.attr.attr. Let's redefine the ARMV8_EVENT_ATTR
> > to simplify the armv8_pmuv3_event_attrs.
> > 
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
> > ---
> >  arch/arm64/kernel/perf_event.c | 189 ++++++++++++++---------------------------
> >  1 file changed, 65 insertions(+), 124 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> > index a0b4f1bca491..d0f084939bcf 100644
> > --- a/arch/arm64/kernel/perf_event.c
> > +++ b/arch/arm64/kernel/perf_event.c
> > @@ -159,132 +159,73 @@ armv8pmu_events_sysfs_show(struct device *dev,
> >  }
> 
> [...]
> 
> > +	(&((struct perf_pmu_events_attr[]) { \
> > +		{ .attr = __ATTR(name, 0444, armv8pmu_events_sysfs_show, NULL), \
> > +		  .id = config, } \
> > +	})[0].attr.attr)
> 
> I don't get the need for the array here. Why can't you do:
> 
> 	(&((struct perf_pmu_events_attr) {
> 		.attr = ...,
> 		.id = ...,
> 	}).attr.attr)

You need want &(obj.attr.attr) rather than &(obj).attr.attr, i.e.

#define ARMV8_EVENT_ATTR(name, config) \
	(&((struct perf_pmu_events_attr) { \
		.attr = __ATTR(name, 0444, armv8pmu_events_sysfs_show, NULL), \
		.id = config, \
	}.attr.attr))

... which compiles for me.

It'd be worth checking that yields a working data structure at runtime.

I'm not sure why I did the array hack in the other PMU drivers -- looks like we
can simplify those assuming this works. :)

THanks,
Mark.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel