netdev - Re: [PATCH] net: Adjust softirq raising in __napi

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Date:	Mon, 26 Oct 2009 08:58:52 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Tilman Schmidt <tilman@...p.cc>,
	David Miller <davem@...emloft.net>, hidave.darkstar@...il.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	linux-wireless@...r.kernel.org, linux-ppp@...r.kernel.org,
	netdev@...r.kernel.org, paulus@...ba.org,
	Michael Buesch <mb@...sch.de>,
	Oliver Hartkopp <oliver@...tkopp.net>
Subject: Re: [PATCH] net: Adjust softirq raising in __napi_schedule

On Mon, 2009-10-26 at 07:54 +0000, Jarek Poplawski wrote:

> > No, I wrote that I didn't know. I suppose now that I looked at it I do
> > know, and only disabling preemption is required.
> 
> But netif_rx has preemption disabled most of the time (by hardirqs
> disabling). So maybe disabling preemption isn't the main reason here
> either?

Not for netpoll though, which may or may not be relevant (if I were to
venture a guess I'd say it isn't and it disables preemption to be able
to do the softirq thing)

However, I lost track now of why we're discussing this.

Basically it boils down to using netif_rx() when in (soft)irq, and
netif_rx_ni() when in process context. That could just be an
optimisation, but it's a very valid one.

johannes

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