netdev - Re: [PATCH 1/1] 3c59x: Acquire vortex lock instead of disabling irq

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Message-Id: <20100317.110320.15445884.davem@davemloft.net>
Date:	Wed, 17 Mar 2010 11:03:20 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	chase.douglas@...onical.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] 3c59x: Acquire vortex lock instead of disabling irq

From: Chase Douglas <chase.douglas@...onical.com>
Date: Wed, 17 Mar 2010 10:33:16 -0400

> Last year, threaded IRQ handlers were introduced to the mainline kernel.
> This change requires the disable_irq function to sleep if any IRQ
> handler threads for a given IRQ line are running.
> 
> Back in 2006, while working on the -rt patch set that had threaded IRQ
> handlers, the vortex_timer function was causing scheduling bugs because
> it is run in softirq context and called disable_irq. This patch was the
> best fix determined at the time, and still exists in the .33 -rt
> patchset. Now that threaded IRQ handlers are present in the mainline
> kernel we need to apply the patch there as well.
> 
> http://lkml.org/lkml/2006/5/12/178
> 
> BugLink: http://bugs.launchpad.net/bugs/533335
> 
> Signed-off-by: Chase Douglas <chase.douglas@...onical.com>

This code is very much intentionally using disable_irq*().

The operation being performed here is extremely expensive,
and during that time if we have cpu interrupts disabled
serial devices will drop characters etc.
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