On Mon, 13 Nov 2000, Thomas D. Dean wrote:

> I am seeing lots of silo overflows in -current SMP.
> #uname -a
> FreeBSD celebris 5.0-CURRENT FreeBSD 5.0-CURRENT #2: \
>   Mon Nov 13 19:31:49 PST 2000 \
>   root@celebris:/usr/src/sys/compile/CELEBRIS-SMP  i386

SMPng has many pessimizations that break sio on slow machines, but I
would have thought that your machine (P5 128MHz?) was fast enough.

With non-SMP kernels, I have only seen silo overflows on my slowest
runnable machine (486DX2/66 with 16450 at 115200 bps.  A 386/20 with
an 8250 at 115200 bps should work).  There is just too much code in
latency-critical code for slow machines to work (on the 486DX2/66,
sio latency is up by a factor of 5-10; sio overheads are only up by
25-50%).  I have unfinished fixes for this.

> I this is not related to the recent patch for conversion to mutex.  I
> tried both ways.

The patches give small or negative optimizations for the SMP case and
not so small pessimizations for the non-SMP case.


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