Re: Warning - running *really* short on DMA buffers while doing file transfers

Justin T. Gibbs
2002-09-26T15:26:38Z

> I reported this same problem some weeks ago -
> http://marc.theaimsgroup.com/?l=linux-kernel&m=103069116227685&w=2 .
> 2.4.20pre kernels solved the error messages flooding the console, and
> improved things a bit, but system load still got very high and disk read
> and write performance was lousy. Adding more memory and using a
> completely different machine didn't help. What did? Changing the Adaptec
> scsi driver to aic7xxx_old . The performance was up 50% for writes and
> 90% for reads, and the system load was acceptable. And i didn't even had
> to change the RedHat kernel (2.4.18-10) for a custom one. The storage was
> two external Arena raid boxes, btw.

I would be interested in knowing if reducing the maximum tag depth for
the driver improves things for you. There is a large difference in the
defaults between the two drivers. It has only reacently come to my
attention that the SCSI layer per-transaction overhead is so high that
you can completely starve the kernel of resources if this setting is too
high. For example, a 4GB system installing RedHat 7.3 could not even
complete an install on a 20 drive system with the default of 253 commands.
The latest version of the aic7xxx driver already sent to Marcelo drops the
default to 32.

--
Justin