linux-kernel - Re: 2.6.20-rc6-mm3

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Message-ID: <20070206220855.GB5109@elte.hu>
Date:	Tue, 6 Feb 2007 23:08:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.20-rc6-mm3


* Daniel Walker <dwalker@...sta.com> wrote:

> > > If we change the current "timer" entry to be listed as 
> > > "lapic-timer" and not "IO-APIC-edge" (or one of the other names) 
> > > and replace it with the count from LOC
[...]
> > But, as per the previous mails, the new behavior is just fine, 
> > because /proc/interrupts just reflects reality. And the way the 
> > kernel utilizes the hardware has just changed - for the better.
> > 
> > The same happens when say a network driver implements NAPI: the IRQ 
> > count goes way, way down. Or if a driver starts supporing MSI - the 
> > IRQ line even moves to another one. Do we try to fix those counts up 
> > to match the 'previous behavior'? Of course not. What you are 
> > suggesting makes no sense, is against current kernel practices - as 
> > we pointed it out to you 7 mails ago.
> 
> I'm not saying we should "fake" anything .. [...]

sorry but that's precisely what your suggestion above results in:

> > > If we change the current "timer" entry to be listed as 
> > > "lapic-timer" and not "IO-APIC-edge" (or one of the other names) 
> > > and replace it with the count from LOC

"replace the timer entry with lapic-timer and put the LOC count there" 
is faking something that does not reflect reality. The 'timer' count is 
for IRQ#0, not for the local apic timer.

> [...] I'm saying list what's really happening .. In a human readable 
> way .

we list precisely what is happening: the number of IRQ#0 interrupts and 
the number of local APIC timer interrupts. Precisely where their 
traditional place is.

i think you might be confused by the generic name that says 'timer'. You 
should notice the other bits that are there too:

           CPU0       CPU1
  0:        495          0   IO-APIC-edge      timer

the '0' means IRQ#0. That makes it clear that this is the PIT timer. 
Clearer now?

	Ingo
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