netdev - Re: request_threaded

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Date:	Fri, 12 Nov 2010 08:35:26 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Mark Ryden <markryde@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: request_threaded_irq()

On Fri, 12 Nov 2010 14:27:11 +0200
Mark Ryden <markryde@...il.com> wrote:

> Hello netdev,
> 
> grepping under net-next-2.6/drivers/net for request_threaded_irq() ,
> shows that it appears only in 3 drivers:
> 
> can/mcp251x.c
> wireless/b43/main.c
> wireless/rt2x00/rt2x00pci.c
> 
> I was wondering: when thinking about performance, is it worthwhile to use this
> API instead of ordinary request_irq() . It seems to me that
> request_threaded_irq()  might
> be better in some cases than NAPI polling forr network drivers (or at
> list it might be so in some systems, maybe multicore ?)

Threaded irq is not needed for properly written NAPI driver.
A NAPI driver should do minimum work in real irq and the whole NAPI processing
will happen in soft-irq.

There has been discussion of moving NAPI softirq into a high
priority thread. But last time I tried it, the performance was noticably
worse on network intensive benchmarks.

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