Re: NFS client latencies

Andrew Morton
2005-03-31T07:18:25Z

Ingo Molnar <mingo@elte.hu> wrote:
>
>
> * Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
>
> > > The 7 ms are spent in this loop:
> >
> > Which is basically confirming what the guys from Bull already told me,
> > namely that the radix tree tag stuff is much less efficient that what
> > we've got now. I never saw their patches, though, so I was curious to
> > try it for myself.
>
> i think the numbers are being misinterpreted. I believe this patch is a
> big step forward. The big thing is that nfs_list_add_request() is O(1)
> now - while _a single request addition to the sorted list_ triggered the
> 1+ msec latency in Lee's previous trace.

Well. The radix-tree approach's best-case is probably quite a lot worse
than the list-based approach's best-case. It hits a lot more cachelines
and involves a lot more code.

But of course the radix-tree's worst-case will be far better than list's.

And presumably that list-based code rarely hits the worst-case, else it
would have been changed by now.