linux-kernel - Re: [PATCH 05/10] nohz: New tick dependency mask

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Message-ID: <20150803130535.GC20269@lerouge>
Date:	Mon, 3 Aug 2015 15:05:37 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 05/10] nohz: New tick dependency mask

On Mon, Aug 03, 2015 at 02:43:50PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 23, 2015 at 06:42:10PM +0200, Frederic Weisbecker wrote:
> > +unsigned long __tick_nohz_set_tick_dependency(enum tick_dependency_bit bit,
> > +					      unsigned long *dep)
> > +{
> > +	unsigned long prev;
> > +	unsigned long old = *dep;
> > +	unsigned long mask = BIT_MASK(bit);
> > +
> > +	while ((prev = cmpxchg(dep, old, old | mask)) != old) {
> > +		old = prev;
> > +		cpu_relax();
> > +	}
> > +
> > +	return prev;
> > +}
> 
> That's typically called a fetch_or(). The function name, which is
> entirely too long, also doesn't suggest a return value.

Nice, I can export fetch_or() from sched code to atomic_fetch_or() like
you just suggested and bring it to asm_generic if you like.
Although given that function name, I fear some people may miss it when they
need such a functionality. I mean, people are interested in a test_and_set_bit()
that returns the whole value. test_and_or() would better recall the test_and_set()
under the line. Now perhaps "test" rather suggests we are dealing with a mask test.
So perhaps fetch_and_or() ? Of course having "and" then "or" in the same function name
might be confusing but after all we have functions names starting with "test" then "and".

Concerning the nohz function name, tick_nohz is a long prefix that is very likely
to produce too long names. Perhaps I should trim tick_nohz to just nohz.
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