linux-kernel - Re: [PATCH v2 3/8] ARCv2: perf: implement "event_set

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Message-ID: <1439920986.28471.13.camel@synopsys.com>
Date:	Tue, 18 Aug 2015 18:03:07 +0000
From:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:	"peterz@...radead.org" <peterz@...radead.org>
CC:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
	"arc-linux-dev@...opsys.com" <arc-linux-dev@...opsys.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"acme@...nel.org" <acme@...nel.org>
Subject: Re: [PATCH v2 3/8] ARCv2: perf: implement "event_set_period" for
 future use with interrupts

Hi Peter,

On Tue, 2015-08-18 at 19:52 +0200, Peter Zijlstra wrote:
> On Wed, Aug 05, 2015 at 06:13:29PM +0300, Alexey Brodkin wrote:
> > Even though this hardware implementation allows for more flexibility,
> > in Linux kernel we decided to mimic behavior of other architectures this
> > way:
> > 
> >  [1] Set limit value as half of counter's max value (to allow counter to
> >      run after reaching it limit, see below for more explanation):
> >  ---------->8-----------
> >  arc_pmu->max_period = (1ULL << counter_size) / 2 - 1ULL;
> >  ---------->8-----------
> 
> > @@ -317,10 +365,11 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
> >  		return -ENOMEM;
> >  
> >  	arc_pmu->n_counters = pct_bcr.c;
> > -	arc_pmu->counter_size = 32 + (pct_bcr.s << 4);
> > +	counter_size = 32 + (pct_bcr.s << 4);
> > +	arc_pmu->max_period = (1ULL << counter_size) - 1ULL;
> >  
> 
> I don't see that /2 there..

My comment was a bit too early.
That "/2" was actually introduced in the subsequent commit.

Do you think I need to do a re-spin of that patch with commit
message which matches real code (i.e. no "/2")?

-Alexey--
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