driver: DMA really really slow

driver: DMA really really slow

Post by Andrew Gabri » Fri, 09 May 2003 16:43:55

Quote:>  194981:DmaBenchmark 0x3fb7f4 bytes, 0.157 sec: 25 mb/s
>  193031:DmaBenchmark 0x3fb7f4 bytes, 0.158 sec: 25 mb/s
>   ...
>  264567:DmaBenchmark 0x3fb7f4 bytes, 0.229 sec: 17 mb/s
>  264257:DmaBenchmark 0x3fb7f4 bytes, 0.229 sec: 17 mb/s

Timings are rather short. Try doubling or halving the amount of
data DMA'ed and see if the timing changes appropriately, or if
you are suffering a significant start or ending overhead.

Andrew Gabriel
Consultant Software Engineer


1. Really, really slow connection to local server via PPP.

Well, this is puzzling--

I've been scratching my head over this for months, reading docs, looking
for non-existent IRQ conflicts because I *thought* I had a problem with
my PCMCIA and/or PPP setup. Just realized that the problem is specific
to *one server*--which happens to be the one I access the most.

* the problem server is in my local domain. It's the one where I have a
shell account (which I often use--or try to use--to ftp stuff back and
forth between home & office), and it's also the primary DNS and the mail
server for the domain.

* the server is an AIX machine which seems up to its job (it's only gone
down once in my 2 years here). When I access it from my office via an
ethernet connection, everything works fine. I can download a multi-meg
file in seconds.

* when I access the net through my PPP connection from home (using a
28.8k PCMCIA modem, dynamic IP addressing), I get reasonable speeds for
http & ftp servers outside the local domain . . . well, slow, but
consistent with what I get in the office.

* when I access this one local server, FTP is mind-numbingly slow (<100
bytes/second!) and I often can't complete a large transfer. Similarly,
if I try to get my mail, it's very slow and tends to stall if there are
a lot of messages.

Any ideas what's causing this? Thanks for any info.

Matt Gushee
Oshamanbe, Hokkaido, Japan

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