linux-kernel - msleep() an load average

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Message-ID: <48D3D52125C49B43AE880038E2E5314BB5BE9D@SRV101.gdsys.de>
Date:	Wed, 4 May 2011 14:11:34 +0200
From:	"Eibach, Dirk" <Eibach@...ys.de>
To:	<linux-kernel@...r.kernel.org>
Subject: msleep() an load average

LDD Chapter 7 says "In general, if you can tolerate longer delays than
requested, you should use schedule_timeout, msleep or ssleep.".

Following this rule, my kernel thread does:
while(1) msleep(1000);

Seconds later userspace guys start whining: "Your driver is evil,
loadavg is 1 and we did not even start our fancy application".

I say: "No, my code is perfectly fine, I followed LDD to the letter."

So the userspace guys head back to their cave, only to return after 5
hours of googling: "Hey, we know what you are doing. Your kernel thread
does uninterruptible sleeps. Wikipedia says, this means you are probably
waiting for disk activity."

Since I don't like having those whining userspace guys around I change
my code, reluctantly:
while(1) msleep_interruptible(1000);

Seconds later they say: "All hail great kernel hacker! You fixed it in
no time."

I appreciate their admiration, but still there are doubts in my mind: Is
this code really any better? Is the loadavg metric broken beyond repair?
Should I really avoid msleep, just to stop those userspace guys from
whining?
The truth must be out there ...

Cheers
Dirk

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