linux-kernel - Re: [Bugme-new] [Bug 12562] New: High overhead while switching or synchronizing threads on different cores

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Date:	Mon, 02 Feb 2009 09:52:11 +0100
From:	Mike Galbraith <efault@....de>
To:	Thomas Pilarski <thomas.pi@...or.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	bugme-daemon@...zilla.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Bugme-new] [Bug 12562] New: High overhead while switching or
	synchronizing threads on different cores

On Mon, 2009-02-02 at 09:33 +0100, Thomas Pilarski wrote:
> Am Montag, den 02.02.2009, 09:19 +0100 schrieb Peter Zijlstra:
> > I suppose you'll have to go bug the glibc people about their random()
> > implementation.
> 
> Yes, I will.

Finding the below was easy enough...

/* POSIX.1c requires that there is mutual exclusion for the `rand' and
   `srand' functions to prevent concurrent calls from modifying common
   data.  */
__libc_lock_define_initialized (static, lock)

...

long int
__random ()
{
  int32_t retval;

  __libc_lock_lock (lock);

  (void) __random_r (&unsafe_state, &retval);

  __libc_lock_unlock (lock);

  return retval;
}

...but finding the plumbing leading to __lll_lock_wait_private()
over-taxed my attention span.

	-Mike

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