linux-kernel - Re: [PATCH 0/2] Kill unused parameter to smp_call

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Message-ID: <20080531204541.GK5405@ucw.cz>
Date:	Sat, 31 May 2008 22:45:42 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, npiggin@...e.de, linux-arch@...r.kernel.org,
	jeremy@...p.org, mingo@...e.hu, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 0/2] Kill unused parameter to smp_call_function and friends

Hi!

> > It bothers me how the smp call functions accept a 'nonatomic' or 'retry'
> > parameter (depending on who you ask), but don't do anything with it.
> > So kill that silly thing.
> > 
> > Two patches here, one for smp_call_function*() and one for on_each_cpu().
> > This patchset applies on top of the generic-ipi patchset just sent out.
> 
> Which leads to notice that we seem to have acquired a bug somewhere on
> the way. smp_call_function on x86 is it seems to me implemented as
> "smp_call_function and occasionally run it multiple times"
> 
> One of the joys of the older x86 APIC setups is the APIC messaging bus.
> This can get checksum errors in which case the message is retransmitted:
> 
> In the specific case a message is retransmitted and there are at least
> three parties on the bus (2 CPU APICs and an IOAPIC is enough) you can
> get a situation where one receiver gets the message the second receiver
> errors it and the retransmit causes the IPI to be repeated which causes
> the IPI to be redelivered.

Does that mean smp_call_function on i386 should have a bitmap of cpus
the message was already delivered to, and drop the duplicates?

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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