linux-kernel - Re: [GIT PULL rcu/next] rcu commits for 2.6.40

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Message-ID: <20110513084253.GE13647@elte.hu>
Date:	Fri, 13 May 2011 10:42:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40


* Yinghai Lu <yinghai@...nel.org> wrote:

> more info:
> if only reverting: e59fb3120becfb36b22ddb8bd27d065d3cdca499
> 
> when compiled with gcc from opensuse 11.3
> [   32.579585] cpu_dev_init done
> [   81.203193] memory_dev_init done
> 
> but when compile that with gcc from fedora 14, then will less delay.
> [   32.404140] cpu_dev_init done
> [   37.602986] memory_dev_init done
> 
> gcc version on opensuse 11.3
> gcc (SUSE Linux) 4.5.0 20100604 [gcc-4_5-branch revision 160292]
> 
> gcc version on fedora 14:
> gcc (GCC) 4.5.1 20100924 (Red Hat 4.5.1-4)

Would it be possible to narrow down it a bit which commit causes the boot 
slowdown?

 known bad : 11c476f31a0f: net,rcu: convert call_rcu(prl_entry_destroy_rcu) to kfree
 known good: 0ee5623f9a6e: Linux 2.6.39-rc6

There's 76 commits inbetween so an about 6-step bisection ought to be able to 
narrow the source of regression down quite a bit ...

The complication with that bisection will be the need to revert the other 
broken commit you found:

 e59fb3120bec: rcu: Decrease memory-barrier usage based on semi-formal proof

Which is unfortunately very early in the series, so you'd have to revert this 
at almost every step of the bisection ...

Thanks,

	Ingo
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