Date: Wed, 14 Jan 2004 00:46:11 +0100
From: Haakon Riiser <hakonrk@ulrik.uio.no>
To: linux-kernel@vger.kernel.org
Subject: Re: Busy-wait delay in qmail 1.03 after upgrading to Linux 2.6
Message-ID: <20040113234611.GA558@s.chello.no>
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References: <20040113210923.GA955@s.chello.no> <20040113135152.3ed26b85.akpm@osdl.org> <20040113232624.GA302@s.chello.no>
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> Output from time:
> 
>   real    0m0.309s
>   user    0m0.011s
>   sys     0m0.004s

Just wanted to comment on my own data, since I just noticed it myself:

The output from time indicates that the system is _not_ using CPU
while delaying, so you might wonder why I said it did.  The reason
is that I'm using an AfterStep applet (ascpu) to monitor CPU usage,
and it appeared to work fine in 2.6.  Now, I see that there are
differences:  For example, another problem I encountered while
upgrading to 2.6 was that disk intensive jobs, such as updating
the slocate database, made ascpu report 100% CPU usage.  I just
ran top (procps 2.0.16) beside it, and it reported approximately
10% CPU usage, which is no more than 2.4 used.

I don't know how ascpu measures CPU usage, but it's interesting
that it appears to work fine for the most part, while giving
_completely_ different results from all other programs (e.g.,
time, top, ps) in the write-delay case, and other disk related
activities.

(For the record, I've never seen ascpu's results differ from
top's under Linux 2.4.x.)

-- 
 Haakon
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