Re: should ia64_spinlock_contention do backoff?

From: Matthew Wilcox <willy_at_debian.org>
Date: 2004-03-29 05:23:57
On Fri, Mar 26, 2004 at 04:14:13PM -0800, Chen, Kenneth W wrote:
> This question is a bit too broad, lock contention highly depends on workload.

Surely.

> For example, I'm doing direct I/O on bunch of block devices, and the dev nodes
> sit on reiserfs, this contention shows up:
> 
>  79.7% 91.2%   18us(1415us)  449us( 760ms)(57.9%)   2970234  8.8% 91.2%    0%  kernel_flag
>  0.00% 92.3%  5.8us(  35us)  689us(  58ms)(0.01%)       298  7.7% 92.3%    0%    __break_lease+0x80

I'm not familiar with this output; I'm assuming this means __break_lease()
is a major contributor to the amount that kernel_flag (ie the BKL)
is locked?  That's interesting; I assume you're using Samba as part of
your workload since it's the only major user of leases that I'm aware of.
Hmm.. seems to me we should move time_out_leases() down 5 lines to minimise
the amount of time we spend with the BKL held if there's a non-lease lock
held on the file.

I wish we'd managed to get the file locking code BKL-free during 2.5 but
it just didn't happen ;-(

-- 
"Next the statesmen will invent cheap lies, putting the blame upon 
the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince 
himself that the war is just, and will thank God for the better sleep 
he enjoys after this process of grotesque self-deception." -- Mark Twain
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Received on Sun Mar 28 14:24:28 2004

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