Linux-kernel mailing list archive 1999-36,: Re: Profiling the kernel?

# Re: Profiling the kernel?

Daniel J Blueman (daniel.j.blueman@stud.umist.ac.uk)
Mon, 6 Sep 1999 21:01:49 +0100

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Hi Thomas,

>Is it possible to profile the kernel? Somewhere there's a bottleneck in my
>system which results in high loads (but top doesn't display the percentages
>correctly, ie idle == 70%, while system load is 0.80 or something) ...
>I suspect it is the IDE subsystem but like to know for sure so I won't
>purchase scsi perpherals for nothing...
Hmm.....

Are your IDE disks setup in DMA mode?
(do a hdparm /dev/hd<harddisk> eg /dev/hda).
If d == 0, then you'd do good to enable DMA transfer **only** if it's safe
to do so (eg Intel chipset, good h/d, etc).

I get very low processor usage (<4%) maxing out the IDE bus and my harddisk
(I get 20.5MB/s to/from it on a Celeron 464A). Of course, the more seeking
done, the less processor time doing I/O (but less transfer rate). This may
imply that it may not be the I/O subsystem. Other tweaks such as 32-bit
transfer, optimal read-ahead, etc help a significant amount AFAICT. Check
the hdparm man page.
(If you were running windows 9x, lots of I/O will draw **lots** of processor
time)

Dan
__________________________
Daniel J Blueman - daniel.j.blueman@stud.umist.ac.uk
Undergraduate - BSc Computing Science
UMIST university - Manchester

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- Next message: Michal Jaegermann: "Re: driver for 3COM USR PCI v.90 modem?"
- Previous message: Chuck Mead: "Adaptec 2920A & fdomain.o (again) (Bugzilla #4670)"
- Maybe in reply to: Thomas van Gulick: "Profiling the kernel?"
- Next in thread: Karim Yaghmour: "Re: Profiling the kernel?"