lkml.org 
[lkml]   [2000]   [Dec]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Abysmal RAID 0 performance on 2.4.0-test10 for IDE?
On Tue, 26 Dec 2000, Felix von Leitner wrote:
> Thus spake Rik van Riel (riel@conectiva.com.br):
> > > One more detail: top says the CPU is 50% system when reading from either
> > > one of the disk or raid devices. That seems awfully high considering
> > > that the Promise controller claims to do UDMA.
> > >
> > > Any comments?
> > Your program reads in data at 30MB/second, on a memory bus
> > that most likely supports something like 60 to 100MB/second.
>
> 100.

So that's 30% for the UDMA controller and maybe
30% for the CPU (if your program reads in all the
data).

> > Part of this memory bandwidth is needed for the UDMA controller
> > to push the data to memory, probably between 30% and 50%.
>
> That would be 30%.

Add to that the overhead of allocating and reclaiming
the memory, doing the RAID mapping, sending commands
to the hard disk, ...

> > Every time the UDMA controller has the memory bus for itself the
> > CPU will busy-wait on memory, which shows up as CPU busy time.
>
> So, you are saying, when I add a gigabit ethernet card, CPU will hit
> 100% at about 30 MB/second? That sounds like a weak architecture ;-)

Hey, there's a reason PCs are so cheap ;)

regards,

Rik
--
Hollywood goes for world dumbination,
Trailer at 11.

http://www.surriel.com/
http://www.conectiva.com/ http://distro.conectiva.com.br/

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:52    [W:0.099 / U:0.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site