Performance issue

Ewan Todd
Mon, 09 May 2005 10:03:18 -0000

> >
> >Whereas, the typical result for the new rig looked more like
> >
> >      105.36 real        71.10 user        33.41 sys
> >     ...
> >     10548  involuntary context switches
> >
> >
>
> First of all, make sure that you have WITNESS and INVARIANTS off in your
> kernel.  You might also want to recompile your kernel with the SMP
> option turned off.
>
> Scott

First of all, thanks to Mike Tancsa for suggesting 5.4 RC4 and to Pete
French for running the test independently on the higher spec machines
with 5.4 RC4 on them, confirming the system time thing, ruling out an
AMD problem, dissociating the system time result from the context
switching, and saving me the trouble of rediscovering the same problem
on 5.4 RC4.

This is my first foray into the public world of FreeBSD discussion
lists, and I am encouraged by the helpfulness of the response.

Scott, the 5.3 kernel I had was a essentially a GENERIC release
kernel, with about 100 options commented out.  WITNESS and INVARIANTS
are off by default, which I confirmed by looking through `sysctl -a`.
However, I was curious to see what I would get if I switched them on,
so I added these options and recompiled the kernel:

  options     KDB
  options     DDB
  options     INVARIANTS
  options     INVARIANT_SUPPORT
  options     WITNESS
  options     WITNESS_SKIPSPIN

The result, below, has essentially the same user time (or just less,
if that makes any sense), but tripled system time.  The context
switches are consistent with the one-per-10msec I saw before.  Is
there anything useful I can do while I still have the kernel debug
options on?

-e


      172.29 real        67.53 user       103.07 sys
     23376  maximum resident set size
       659  average shared memory size
     20805  average unshared data size
       127  average unshared stack size
      5402  page reclaims
         0  page faults
         0  swaps
         0  block input operations
         0  block output operations
         0  messages sent
         0  messages received
         0  signals received
         0  voluntary context switches
     17234  involuntary context switches