Message-ID: <4AE56217.3040708@imap.cc>
Date: Mon, 26 Oct 2009 10:47:19 +0200
From: Tilman Schmidt <tilman@imap.cc>
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To: Johannes Berg <johannes@sipsolutions.net>
CC: Jarek Poplawski <jarkao2@gmail.com>, David Miller <davem@davemloft.net>,
       hidave.darkstar@gmail.com, linux-kernel@vger.kernel.org,
       tglx@linutronix.de, linux-wireless@vger.kernel.org,
       linux-ppp@vger.kernel.org, netdev@vger.kernel.org, paulus@samba.org,
       Michael Buesch <mb@bu3sch.de>, Oliver Hartkopp <oliver@hartkopp.net>
Subject: Re: [PATCH] net: Adjust softirq raising in __napi_schedule
References: <4AD76184.6030900@gmail.com> <4ADF5710.4030505@imap.cc>	 <20091021211906.GA11401@ami.dom.local>	 <1256160330.12174.2.camel@johannes.local>	 <20091021213947.GA12202@ami.dom.local>	 <1256200021.12174.11.camel@johannes.local> <4AE1C00B.5010008@imap.cc>	 <1256309191.12174.51.camel@johannes.local>	 <20091026074126.GA6187@ff.dom.local>	 <1256543054.28230.6.camel@johannes.local>	 <20091026075438.GB6187@ff.dom.local> <1256543932.28230.9.camel@johannes.local>
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Am 26.10.2009 09:58 schrieb Johannes Berg:
> 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.

The starting point were several reports of the kernel message:

NOHZ: local_softirq_pending 08

Originally most if not all of them came from wireless networking,
but I muddied the waters by adding to the mix a case involving ISDN.
You stated that all the solutions proposed so far were wrong, so
we're naturally turning to you for guidance on what the right
solution might be.

> 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.

Hmmm. That seems to contradict your earlier statement to me that
simply replacing a call to netif_rx() by one to netif_rx_ni()
when not in interrupt context isn't a valid solution either.
What am I missing?

Thanks,
Tilman

- --
Tilman Schmidt                    E-Mail: tilman@imap.cc
Bonn, Germany
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