linux-kernel - Re: [PATCH] drivers: CCI: fix used_mask init in validate

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Message-ID: <20150409144029.GE9648@leverpostej>
Date:	Thu, 9 Apr 2015 15:40:29 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Mark Salter <msalter@...hat.com>
Cc:	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] drivers: CCI: fix used_mask init in validate_group()

> > > > >  validate_group(struct perf_event *event)
> > > > >  {
> > > > >  	struct perf_event *sibling, *leader = event->group_leader;
> > > > > -	struct cci_pmu_hw_events fake_pmu = {
> > > > > -		/*
> > > > > -		 * Initialise the fake PMU. We only need to populate the
> > > > > -		 * used_mask for the purposes of validation.
> > > > > -		 */
> > > > > -		.used_mask = CPU_BITS_NONE,
> > > > 
> > > > Can we not simply change this to:
> > > > 
> > > > 		.used_mask = { 0 },
> > > > 
> > > > That should result in the entire array being zeroed.
> > > 
> > > It does, but it also causes the whole struct to be cleared.
> > 
> > Sure, but it's also the minimal diff, and it's easier to read. This was
> > what the code was intended to be initially.
> > 
> > > With the memset, only used_mask gets cleared.
> > 
> > Is there an appreciable difference between the two performance-wise?
> 
> I dunno. It is 3 strp insns vs 1 str.
> If you want the static init, I'll send another patch.

I'd prefer the designated initializer to the memset.

Thanks,
Mark.
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