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Date: Sat, 30 Dec 2000 14:25:49 -0500 (EST)
From: Alexander Viro <viro@math.psu.edu>
To: Linus Torvalds <torvalds@transmeta.com>
cc: linux-kernel@vger.kernel.org
Subject: Re: 2.2.19pre3 and poor reponse to RT-scheduled processes?
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On 30 Dec 2000, Linus Torvalds wrote:

> There are other, equally likely, candidates for these kinds of stalls:
> 
>  - filesystem locks. Especially the ext2 superblock lock. You can easily
>    hit this one, as some ext2 functions actually do a lot of IO while
>    holding the lock.

Hmm... In 2.4 we can make the situation with superblock lock on ext2
much better. I didn't go the whole way down to spinlocks, but right now
I'm sitting on a box with modified ext2 that doesn't do _any_ IO in
protected parts of ext2_new_inode()/ext2_new_block(). I can try to
extract the relevant parts of the patch if you are interested (it also
got directories-in-pagecache stuff and better SMP threading of
get_block()/truncate()). The thing seems to be working fine and I see
no serious contention on lock_super(). Dunno if it's worth doing before
2.4.0, but since it has zero impact on the rest of tree (OK, zero except
that write_on_page() had been exported, but I could trivially get rid
of that)... Maybe 2.4.early would be a good idea.
							Cheers,
								Al

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