linux-kernel - Re: [PATCH 04/10] idr: Percpu ida

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Message-ID: <20130807183345.GA11612@kmo-pixel>
Date:	Wed, 7 Aug 2013 11:33:45 -0700
From:	Kent Overstreet <kmo@...erainc.com>
To:	Christoph Lameter <cl@...two.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Jens Axboe <axboe@...nel.dk>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Subject: Re: [PATCH 04/10] idr: Percpu ida

On Wed, Aug 07, 2013 at 05:56:34PM +0000, Christoph Lameter wrote:
> On Wed, 7 Aug 2013, Kent Overstreet wrote:
> 
> > +{
> > +	DEFINE_WAIT(wait);
> > +	struct percpu_ida_cpu *tags;
> > +	unsigned long flags;
> > +	unsigned this_cpu;
> > +	int tag;
> > +
> > +	local_irq_save(flags);
> 
> > +	this_cpu = smp_processor_id();
> > +	tags = per_cpu_ptr(pool->tag_cpu, this_cpu);
> 
> tags = this_cpu_ptr(pool->tag_cpu);

I was breaking it apart because I was using this_cpu elsewhere too - for
the bitmap of which cpus have non empty freelists.

Or is this_cpu_ptr() doing something smarter than per_cpu_ptr(ptr,
smp_processer_id())? There's so many variants I'm not 100% sure they're
the same.
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