Messages in this thread |  | | Date | Tue, 26 Dec 2000 14:35:39 -0200 (BRDT) | From | Rik van Riel <> | Subject | Re: Abysmal RAID 0 performance on 2.4.0-test10 for IDE? |
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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/
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