I have been investigating what the cause of performance loss could be.
I have noticed several things:
0) Setting to CARM_MAX_Q to 30 hangs. So we have been testing only with
CARM_MAX_Q == 1. The firmware has not been updated yet.
1) If we keep on increasing number of SATA disks, hdparm does not get
multiplied total read performance (hdparm -t ....).
With a Maxtor 60 GB disk with 8MB cache we get 50Mb/sec. If we put
two disks we get 35 on each. Total 70MB/sec. If we put more
then total does not get above 70MB/sec.
It looks like that a part of the driver serializes the commands.
We have a 32 processor MIPS based system.
2) It looks like that there is while(1) loop under spinlock in isr
stack. If we start queuing many commands then it may take a while for
this loop to break. Though I am not quite familiar with the driver yet.
If we set CARM_MAX_Q to 30 then the request/response queue length should
also be increased right?
3) Next I will put PCI-X analyzer and figure out the root cause of
performance loss. May be need to get hold of the technical manual.
Kallol
On Sun, 2005-06-12 at 09:30, Mark Lord wrote:
> [email protected] wrote:
> >
> >
> > Hello Jeff,
> > How did you verify that performance improved making the
> > changes those
> > you suggested?
> >
> > hdparm does not show it.
>
> My hdparm tool performs a single I/O at a time,
> disregarding any kernel read-ahead that may be added on.
>
> As such, it won't often show the effects of queued commands
> as well as some other test might.
>
> Cheers
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