From: David Miller <davem@davemloft•net>
To: paulus@samba•org
Cc: linuxppc-dev@ozlabs•org
Subject: Re: question about softirqs
Date: Fri, 08 May 2009 16:53:58 -0700 (PDT) [thread overview]
Message-ID: <20090508.165358.97542490.davem@davemloft.net> (raw)
In-Reply-To: <18948.49541.735156.176919@cargo.ozlabs.ibm.com>
From: Paul Mackerras <paulus@samba•org>
Date: Sat, 9 May 2009 09:34:29 +1000
> If a soft irq is raised in process context, raise_softirq() in
> kernel/softirq.c calls wakeup_softirqd() to make sure that ksoftirqd
> runs soon to process the soft irq. So what would happen is that we
> would see the TIF_RESCHED_PENDING flag on the current task in the
> syscall exit path and call schedule() which would switch to ksoftirqd
> to process the soft irq (if it hasn't already been processed by that
> stage).
>
> If the soft irq is raised in interrupt context, then the soft irq gets
> run via the do_softirq() call in irq_exit(), as you saw.
>
> The soft irq stuff is pretty much all generic code these days, except
> for the code to switch to the softirq stack.
Grumble, when did that happen :-(
That's horrible for latency compared to handling it directly
in the trap return path.
next prev parent reply other threads:[~2009-05-08 23:54 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-08 22:51 question about softirqs Chris Friesen
2009-05-08 23:05 ` David Miller
2009-05-08 23:34 ` Paul Mackerras
2009-05-08 23:53 ` David Miller [this message]
2009-05-09 2:52 ` Benjamin Herrenschmidt
2009-05-09 3:31 ` Paul Mackerras
2009-05-09 6:48 ` David Miller
2009-05-11 18:25 ` Chris Friesen
2009-05-11 23:24 ` David Miller
2009-05-12 0:43 ` 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
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
2009-05-11 23:34 ` Paul Mackerras
2009-05-09 0:28 ` Chris Friesen
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