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

From: Ingo Molnar
Date: Fri May 13 2011 - 04:43:19 EST



* Yinghai Lu <yinghai@xxxxxxxxxx> 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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