Re: [PATCH 1/3] sysfs directory scaling: rbtree for dirent name lookups

From: Benjamin LaHaise
Date: Tue Nov 03 2009 - 16:52:58 EST

On Tue, Nov 03, 2009 at 01:32:33PM -0800, Eric W. Biederman wrote:
> Are your numbers from your application and are they real world?
> In which case they are interesting, but it would be good if
> we could also have microbenchmark numbers that just measure
> the sysfs costs. If nothing else I am seeing a big startup
> overhead that isn't being subtracted out that makes it hard
> to see the real costs here.

They're application based, so there's a bunch of other overhead included
that won't show up on a microbenchmark. Each interface requires a round
trip between 2 L2TP daemons, so there are lots of syscalls and other cache
polluting effects that won't show up on a microbenchmark. One of the L2TP
daemons is configured not to instantiate any kernel state -- running in
this mode, it has very little overhead.

The other thing to note is that the costs posted are how long it takes to
add an additional 5,000 interfaces in the given range, not the total time
to add say 35,000 interfaces (I didn't feel like waiting that long).

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