Re: Google Summer of Code Project: Port OpenAFS Client

[christos%astron.com@localhost (Christos Zoulas)]

In article <20100331160328.GC2955%cs.hut.fi@localhost>,
Antti Kantee  <pooka%cs.hut.fi@localhost> wrote:
>On Wed Mar 31 2010 at 15:37:37 +0000, Christos Zoulas wrote:
>> As for the performance of the server I think it depends on the workload
>> (how many kernel-userland transitions you end up doing, and how agressive
>> is your "attribute cache" to use NFS lingo).
>
>While attribute caching in the file server does matter (network latency,
>disk latency, what have you), I haven't stumbled across a workload where
>lack of kernel attribute caching has any significant impact.  I'm not
>saying an application scenario doesn't exist, just that I haven't run
>into one.

Any tree walkers... find, rdist, rsync, sup, tar, pax, cpio that do more
stat() than I/O under certain conditions (filtering etc.). Try to run:

        find /amd/remote/root -type f -name slow -print

with /amd/ being an automounted directory and /remote/ a symlink to the nfs
mounted partition, and see amd's cpu going 100%. This is why I had to add
code to set the automounted directory attribute cache time. Even setting it
to 1 second fixes the problem. Having it 0 is a disaster.

christos