netdev - Re: [PATCH] r8169: avoid NAPI scheduling delay.

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Date:	Sun, 10 Jun 2012 20:21:28 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	romieu@...zoreil.com
Cc:	netdev@...r.kernel.org, davej@...hat.com, marc.c.dionne@...il.com,
	tglx@...utronix.de, js@...21.net, realnc@...il.com,
	hayeswang@...ltek.com
Subject: Re: [PATCH] r8169: avoid NAPI scheduling delay.

From: Francois Romieu <romieu@...zoreil.com>
Date: Sat, 9 Jun 2012 22:53:16 +0200

> While reworking the r8169 driver a few months ago to perform the
> smallest amount of work in the irq handler, I took care of avoiding
> any irq mask register operation in the slow work dedicated user
> context thread. The slow work thread scheduled an extra round of NAPI
> work which would ultimately set the irq mask register as required,
> thus keeping such irq mask operations in the NAPI handler.
> It would eventually race with the irq handler and delay NAPI execution
> for - assuming no further irq - a whole ksoftirqd period. Mildly a
> problem for rare link changes or corner case PCI events.
> 
> The race was always lost after the last bh disabling lock had been
> removed from the work thread and people started wondering where those
> pesky "NOHZ: local_softirq_pending 08" messages came from.
> 
> Actually the irq mask register _can_ be set up directly in the slow
> work thread.
> 
> Signed-off-by: Francois Romieu <romieu@...zoreil.com>
> Reported-by: Dave Jones <davej@...hat.com>
> Tested-by: Marc Dionne <marc.c.dionne@...il.com>

Applied, thanks.
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