Re: (disk/cpu) kernel performance problem

Mark Lord (mlord@pobox.com)
Tue, 27 Jul 1999 20:30:59 -0400

Gerald Aigner wrote:
...
> Yes, DMA is enabled. Please keep in mind that I am reading something like
> 25-30 MB/second from the disks.
>
> I know that 45% (or in the case of 2.3.11 37%) is high and that's why
> I ask. I really would like to have these cycles to do my calculations.

The 45% doesn't mean much by itself.

What does "hdparm -T" give you?
(Uppercase T -- times memory/filesystem
throughput, without accessing the device).

If it gives something like 60-70MB/sec,
then your 25-30 is indeed 45% of your memory bandwidth.

Eg. My P2-400 with IDE drives gives 22MB/sec reading
from the drives, chewing up 14-18% of the CPU, mostly in copying
memory around. The -T thingie gives 116MB/sec, so we have:

22 / 116 = 18%

The darned thing even makes sense, given sufficient context.

-- 
Mark Lord
Real-Time Remedies Inc.
mlord@pobox.com


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