netdev - Re: mac80211: NOHZ: local_softirq

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Message-ID: <4AC3475C.7000403@hartkopp.net>
Date:	Wed, 30 Sep 2009 13:56:12 +0200
From:	Oliver Hartkopp <socketcan@...tkopp.net>
To:	"John W. Linville" <linville@...driver.com>
CC:	Michael Buesch <mb@...sch.de>, Kalle Valo <kalle.valo@....fi>,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	Johannes Berg <johannes@...solutions.net>
Subject: Re: mac80211: NOHZ: local_softirq_pending 08

John W. Linville wrote:
> On Sat, Sep 12, 2009 at 06:41:12PM +0200, Oliver Hartkopp wrote:
> 
>> i cooked a patch that introduces netif_rx_ti() and fixes up the problems in
>> mac80211 and the CAN subsystem.
> 
> Oliver,
> 
> Are you going to send this patch to Dave?  If you want me to carry
> it instead, please resend it with a proper changelog including a
> Signed-off-by line.  For that matter, Dave will most certainly want
> that as well...

Hello John,

as i wrote here

http://marc.info/?l=linux-netdev&m=125277885910179&w=2

there are currently only three occurrences of checks that use netif_rx() and
netif_rx_ni() depending on in_interrupt().

And regarding the suggested fix from Michael, that checked every(!) netif_rx()
whether it is in interrupt or not, i was unsure if a netif_tx_ti() would make
sense for only three cases?!?

If you think it makes sense, i can post a patch for that ... but:

Indeed it costs some additional investigation to prove whether netif_rx() or
netif_rx_ni() should be used in each case. But IMHO this has to be done before
providing a pump-gun function that solves the problem without thinking if we
are in irq-context or not. I want to avoid that people are using netif_rx_ti()
as some kind of default ...

I don't know how expensive in_interrupt() is, but it IMO should be avoided
when the context for a code section can be determined in another way.

Regards,
Oliver

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