linux-kernel - Re: [PATCH resend] cpumask: don't perform while loop in cpumask_next

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Message-ID: <20150615134008.GA4447@pd.tnic>
Date:	Mon, 15 Jun 2015 15:40:08 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Amir Vadai <amirv@...lanox.com>, linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH resend] cpumask: don't perform while loop in
 cpumask_next_and()

On Mon, Jun 15, 2015 at 03:12:21PM +0200, Peter Zijlstra wrote:
> On Mon, Mar 02, 2015 at 12:22:03AM +0900, Sergey Senozhatsky wrote:
> 
> > +++ b/lib/cpumask.c
> > @@ -37,10 +37,11 @@ EXPORT_SYMBOL(__next_cpu_nr);
> >  int cpumask_next_and(int n, const struct cpumask *src1p,
> >  		     const struct cpumask *src2p)
> >  {
> > +	struct cpumask tmp;
> > +
> > +	if (cpumask_and(&tmp, src1p, src2p))
> > +		return cpumask_next(n, &tmp);
> > +	return nr_cpu_ids;
> >  }
> >  EXPORT_SYMBOL(cpumask_next_and);
> 
> Just ran into this; I though we were not supposed to put cpumasks on the
> stack because $BIG. ?!
> 
> explain.

That's some fat stack with 8K CPUs:

cpumask_next_and:
        pushq   %rbp    #
        movq    %rsp, %rbp      #,
        pushq   %rbx    #
        movl    %edi, %ebx      # n, n
        leaq    -1040(%rbp), %rdi       #, tmp106
        subq    $1032, %rsp     #,
		^^^^^

Lovely.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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