Linux-kernel mailing list archive 1999-36,: Re: Fixing the SCSI layer

# Re: Fixing the SCSI layer

Gerard Roudier (groudier@club-internet.fr)
Sun, 5 Sep 1999 10:57:41 +0200 (MET DST)

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On Sun, 5 Sep 1999, Alan Cox wrote:

> > Besides, cleaning up the code, has anyone identified specific performance
> > problems that need to be fixed in the SCSI mid-layer? For some reason the
> > Interphase FC adapter is topping out at ~72MB/s on sequential reads,
> > this seems rather low, knowing that we can get 90+ with identical hardware
> > under NT.
>
> The code is too heavy weight. I See performance limits with the Symbios
> FC card too. In paticular the commands/second is very very limited.

Depends on the number of commands per seconds you need.

I can get up to 13000 actual 1K I/O READs per seconds on a single LVD BUS
with useless kernel buffering under 2.0.36 using 2 fast disks and 2 reader
processes (1 per device to overlap driver+controller+interrupt+etc...
latencies). I just disable readahead for the block devices and read 1K
chunck at a time. May-be I could get slightly more cmds/sec by eliminating
kernel buffering (or under recent kernel), but I am too lazy to hack for
that.

The machine is a PII/233 with 66MHz system bus and 33 MHz 32bit PCI BUS,
controller can be a SYM53C896 or 895.

In my immediate opinion, it could well be some latency in some device,
likely the controller, that makes the commands/second throughput not being
as good as you expect.

Gérard.

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