priority-- curious about cpu resouce share

[Sergey 'DoubleF' Zaharchenko]

On Wed, 03 Mar 2004 00:34:37 +0800
"Zhang Weiwu" <weiwuzhang at hotmail.com> probably wrote:

> Today I did't experiment on {rt|id}prio(1), just to be interesting. I am 
> trying to understand FreeBSD priority mechenism. IMHO realtime/idle 
> priority only starvs processes when there is no cpu resource at all. 
> 
> To test, I run mpg321 on realtime priority 3, run ppp on realtime priority 
> 4, a little lower than mpg321, and scp over the ppp tunnel on normal 
> priority. 
> 
> Top(1) shows an average about:
> 55.2% user,  0.0% nice, 21.5% system, 12.2% interrupt, 11.1% idle
> * mpg321 takes average about 70%;
> * ppp is seriously slowed down, it takes about 1.5% (normally 17% on full 
> speed);
> * sshd almost starves; it takes 0.00% (normally 2%) and only transfer 
> several bytes once several minutes; the otherside scp prompts "stalled".

sshd doesn't starve CPU, I guess; as you reach it through ppp, and ppp
gets slow, sshd does, too.

> I'm the kind of newbie think 11.1% idle cpu time to be free cpu resource, 
> because I don't have idle process. I wish to know why, as there are still 
> 11.1% free cpu resource, ppp and sshd doesn't get this share? 

The most frequent cause is that they don't need the CPU so much as
something else, like disk I/O, etc. Could you please post the whole
output of top (and a snapshot of systat -vmstat, for example)?

> Just to be curious. Thank you.

FWIW, splay uses <30% of a P150:)

-- 
DoubleF
A jury consists of 12 persons chosen to decide
who has the better lawyer.
		-- Robert Frost
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