From: Thomas Gleixner <tglx@linutronix.de>
To: Andi Kleen <andi@firstfloor.org>
Cc: Chris Friesen <cfriesen@nortel.com>, Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Steven Rostedt <rostedt@goodmis.org>,
David Miller <davem@davemloft.net>,
linuxppc-dev@ozlabs.org, paulus@samba.org,
netdev@vger.kernel.org
Subject: Re: question about softirqs
Date: Wed, 13 May 2009 16:17:08 +0200 (CEST) [thread overview]
Message-ID: <alpine.LFD.2.00.0905131612180.3561@localhost.localdomain> (raw)
In-Reply-To: <20090513141532.GT19296@one.firstfloor.org>
On Wed, 13 May 2009, Andi Kleen wrote:
> > "If a soft irq is raised in process context, raise_softirq() in
> > kernel/softirq.c calls wakeup_softirqd() to make sure that ksoftirqd
>
> softirqd is only used when the softirq runs for too long or when
> there are no suitable irq exits for a long time.
>
> In normal situations (not excessive time in softirq) they don't
> do anything.
Err, no. Chris is completely correct:
if (!in_interrupt())
wakeup_softirqd();
We can not rely on irqs coming in when the softirq is raised from
thread context. An irq_exit might be faster to process it than the
scheduler can schedule ksoftirqd in, but ksoftirqd is woken and runs
nevertheless. If it finds a softirq pending then it processes them in
it's context and irq_exit calls to softirq are returning right away.
Thanks,
tglx
next prev parent reply other threads:[~2009-05-13 14:18 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <18948.63755.279732.294842@cargo.ozlabs.ibm.com>
[not found] ` <20090508.234815.127227651.davem@davemloft.net>
[not found] ` <4A086DB2.8040703@nortel.com>
[not found] ` <20090511.162436.193717082.davem@davemloft.net>
2009-05-12 0:43 ` question about softirqs Chris Friesen
2009-05-12 8:12 ` Ingo Molnar
2009-05-12 9:12 ` Peter Zijlstra
2009-05-12 9:23 ` Ingo Molnar
2009-05-12 9:32 ` Peter Zijlstra
2009-05-12 12:20 ` Steven Rostedt
2009-05-13 4:45 ` David Miller
2009-05-13 4:44 ` David Miller
2009-05-13 5:15 ` Paul Mackerras
2009-05-13 5:28 ` David Miller
2009-05-13 5:55 ` Evgeniy Polyakov
2009-05-12 15:18 ` Chris Friesen
2009-05-13 8:34 ` Andi Kleen
2009-05-13 13:23 ` Chris Friesen
2009-05-13 14:15 ` Andi Kleen
2009-05-13 14:17 ` Thomas Gleixner [this message]
2009-05-13 14:24 ` Andi Kleen
2009-05-13 14:54 ` Eric Dumazet
2009-05-13 15:02 ` Andi Kleen
2009-05-13 15:05 ` Chris Friesen
2009-05-13 15:54 ` Thomas Gleixner
2009-05-13 16:10 ` Chris Friesen
2009-05-13 17:01 ` Andi Kleen
2009-05-13 19:04 ` Chris Friesen
2009-05-13 19:13 ` Andi Kleen
2009-05-13 19:44 ` Chris Friesen
2009-05-13 19:53 ` Andi Kleen
2009-05-13 20:55 ` Thomas Gleixner
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