Niels Kobschätzki wrote:
>sorry for the cross-posting but so far I had no real luck on the forum
>or on question, thus I want to try my luck here as well.
I read email lists but don't do the other stuff, so I just saw this yesterday.
Short answer, I haven't a clue why cache hits rate would have changed.

The code that decides if there is a hit/miss for the attribute cache is in
ncl_getattrcache() and the code hasn't changed between 10.3->11.1,
except the old code did a mtx_lock(&Giant), but I can't imagine how that
would affect the code.

You might want to:
# sysctl -a | fgrep vfs.nfs
for both the 10.3 and 11.1 systems, to check if any defaults have somehow
been changed. (I don't recall any being changed, but??)

If you go into ncl_getattrcache() {it's in sys/fs/nfsclient/nfs_clsubs.c}
and add a printf() for "time_second" and "np->n_mtime.tv_sec" near the
top, where it calculates "timeo" from it.
Running this hacked kernel might show you if either of these fields is bogus.
(You could then printf() "timeo" and "np->n_attrtimeo" just before the "if"
clause that increments "attrcache_misses", which is where the cache misses
happen to see why it is missing the cache.)
If you could do this for the 10.3 kernel as well, this might indicate why the
miss rate has increased?

>I upgraded a machine from 10.3-Prerelease (custom kernel with
>tcp_fastopen added) to 11.1-Release (standard kernel) with
>freebsd-update. I have two other machines that are still on
>10.3-Prerelease. Those machines mount an NFS-export from a
>Linux-NFS-server and use NFSv3. The machine that got upgraded shows now
>far more cache misses for getattr than on the 10.3-machines (we talk a
>factor of 100) in munin. munin also shows a lot more cache-misses for
>other metrics like biow, biorl, biod (where can I find what those
>metrics mean…currently I have not even an understanding what these are)
>Can anybody help me how I can debug this problem or has an idea what
>could cause the problem? The result of this behavior is that this
>machine shows a lower performance than the others and I cannot upgrade
>other machines before I didn't fix this bug.
I haven't run a 10.x system in quite a while. When I get home in a few days,
I might be able to reproduce this. If I can. I can poke at it, but it would be 
least a week before I might have an answer and I may not figure it out for a
long time.

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