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Date: Mon, 11 May 2009 18:43:27 -0600 From: "Chris Friesen" <cfriesen@...tel.com> To: David Miller <davem@...emloft.net> CC: linuxppc-dev@...abs.org, paulus@...ba.org, netdev@...r.kernel.org, Ingo Molnar <mingo@...e.hu> Subject: Re: question about softirqs This started out as a thread on the ppc list, but on the suggestion of DaveM and Paul Mackerras I'm expanding the receiver list a bit. Currently, if a softirq is raised in process context the TIF_RESCHED_PENDING flag gets set and on return to userspace we run the scheduler, expecting it to switch to ksoftirqd to handle the softirqd processing. I think I see a possible problem with this. Suppose I have a SCHED_FIFO task spinning on recvmsg() with MSG_DONTWAIT set. Under the scenario above, schedule() would re-run the spinning task rather than ksoftirqd, thus preventing any incoming packets from 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. DaveM pointed out that if we're doing transmits we're likely to hit local_bh_enable(), which would process the softirq work. However, I think we may still have a problem in the above rx-only scenario--or is it too contrived to matter? Thanks, Chris -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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