Re: [PATCH] anobjrmap 9 priority mjb tree

[Hugh Dickins]

On Fri, 9 Apr 2004, Martin J. Bligh wrote:
> >> This slows down kernel compile a little, but worse, it slows down SDET
> >> by about 25% (on the 16x). I think you did something horrible to sem
> >> contention ... presumably i_shared_sem, which SDET was fighting with
> >> as it was anyway ;-(
> >> 
> >> Diffprofile shows:
> >> 
> >>     122626    15.7% total
> >>      44129   790.0% __down
> >>      20988     4.1% default_idle
> 
> I applied Andrew's high sophisticated proprietary semtrace technology.

Thanks a lot, Martin, this seems pretty important.

So, i_shared_sem, as you supposed.

Do you still have the two profiles input to diffprofile?
I wonder if they'd have clues to help us understand it better.

Any chance of you doing the same comparison between 2.6.5-aa5 
2.6.5-aa5 minus prio-tree?  (Well, needn't be -aa5, whatever comes to
hand.  Looks like "patch -p1 -R < prio-tree" mostly works, just some
rejects in mm/mmap.c itself, let me know if I can help out on that.)

If -aa is okay, I hope so, then it's surely some stupidity from me.

We're not at all surprised that vma linking and unlinking should take
rather longer; but the rise in __down, __wake_up, finish_task_switch
is horrifying.  Or is that how it usually looks, when a semaphore is
well contended - thundering herd?

Hugh

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