2000-12-20 15:26:36

by Alberto Bertogli

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Subject: Weird vmstat reports in 2.2.18

I'm getting some strange reports with vmstat on a dual iPPro running 2.2.18,
it doesnt happen very frequently, but i see it a lot when compiling something
(kernel and mysql specially, not when compiling small stuff), though it doesnt
look like a high-load issue. When the machine is idle (ie. most of the time at
the moment) it doesnt show up.

The report is like this:
#vmstat 1 60 | awk '{ print $16 }'
id
0
0
20452224
1
20452224
0
1
20452224
1
0
0

I wasnt able to trigger it in a predictable way, it just pops up...
BUT if i open two vmstats in different consoles.. the number doesnt show up in
both, just in one of them... so i'm not sure at all if this is a kernel bug, or
just another (vmstat?) feature =)
I also found a reference to something similar in
http://www.uwsg.iu.edu/hypermail/linux/kernel/0009.3/0273.html

Alberto


2000-12-21 12:56:45

by john slee

[permalink] [raw]
Subject: Re: Weird vmstat reports in 2.2.18

On Wed, Dec 20, 2000 at 11:55:37AM -0300, [email protected] wrote:
> I'm getting some strange reports with vmstat on a dual iPPro running 2.2.18,
> it doesnt happen very frequently, but i see it a lot when compiling something
> (kernel and mysql specially, not when compiling small stuff), though it doesnt
> look like a high-load issue. When the machine is idle (ie. most of the time at
> the moment) it doesnt show up.

i can consistently produce this on dual p3 600/2.2.17pre20. in my case
it's the `ab' benchmark tool supplied with apache that helps reproduce
it. incidentally i only noticed this in the last day or two, good to
know i'm not the only one. :-)

our setup is apache/php/postgresql. fairly intensive pages. i start
seeing vmstat oddities after about 15 concurrent requests.

> I wasnt able to trigger it in a predictable way, it just pops up...
> BUT if i open two vmstats in different consoles.. the number doesnt show up in
> both, just in one of them... so i'm not sure at all if this is a kernel bug, or
> just another (vmstat?) feature =)

the vmstat processes probably aren't reading /proc/* at exactly the same
time, so the numbers they see will likely be different...

j.