From: "Chris Friesen" <cfriesen@nortel•com>
To: Paul Mackerras <paulus@samba•org>
Cc: linuxppc-dev@ozlabs•org
Subject: Re: question about softirqs
Date: Fri, 08 May 2009 18:28:58 -0600 [thread overview]
Message-ID: <4A04CE4A.9080709@nortel.com> (raw)
In-Reply-To: <18948.49541.735156.176919@cargo.ozlabs.ibm.com>
Paul Mackerras wrote:
> 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).
I think I see a problem with this. Suppose I have a SCHED_FIFO task
spinning on recvmsg() with MSG_DONTWAIT set (and maybe doing other stuff
if there are no messages). Under the scenario you described, schedule()
would re-run the spinning task, no? This could prevent any incoming
packets from actually being sent up the stack until we get a real
hardware interrupt--which could be a whole jiffy if interrupt mitigation
is enabled in the net device.
Chris
prev parent reply other threads:[~2009-05-09 0:29 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
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 [this message]
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