Re: 2.6.4 : 100% CPU use on EIDE disk operarion, VIA chipset

Bill Davidsen
2004-04-03T12:49:46Z

> Mikhail Ramendik wrote:
>
>> Hello,
>>
>> I have an computer with an AMD Duron, and the motehrboard chipset is VIA
>> KT133. The hard drive is a Seagate Barracuda 7200.7 ; no other EIDE
>> devices are attached.
>>
>> I run an RH9-based distro, and added a 2.6.4 kernel to it. The following
>> problem was tested with two kernel variants: 2.6.4+wolk2/0 with
>> preeemption enabled, and 2.6.4 plain from kernel.org with preemption
>> disabled. No difference.
>>
>> I noticed performance problems with 2.6.4, and tracked them to strange
>> HDD behavior.
>>
>> It turned out that on disk-intensive operation, the "system" CPU usage
>> skyrockets. With a mere "cp" of a large file to the same direstory
>> (tested with ext3fs and FAT32 file systems), it is 100% practically all
>> of the time !
>
>
> Which tool do you use for measure? xosview?
>
> I'm having here the same problem. But it depends on the tool which is
> used for measuring. If I use top from procps 3.2, I can't see this high
> system load. "time" can't see it, too.
>
> This is what top says during cp of 512MB-file:
> Cpu(s): 2.0% us, 8.3% sy, 0.0% ni, 0.0% id, 89.0% wa, 0.7% hi,
> 0.0% si
>
> New is "wa", what probably means "wait". This value is very high as long
> as the HD is writing or reading datas:
>
> cp dummy /dev/null
> produces this top-line:
> Cpu(s): 3.0% us, 5.3% sy, 0.0% ni, 0.0% id, 91.0% wa, 0.7% hi,
> 0.0% si

Yes "wa" is not intuitive, some other operating systems use "wio" for
"wait i/o" time. As noted in the other thread, you can try the deadline
elevator or increased readahead for your load.
>
> and time says:
> real 0m53.195s
> user 0m0.013s
> sys 0m2.124s
>
>
> But you're right, 2.6.4 is slower than 2.4.25. See the thread "Very poor
> performance with 2.6.4" here in the list.

Much discussed, not overly fixed :-(

--
bill davidsen <davidsen@tmr.com>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979