Messages in this thread | | | Date | Fri, 11 Apr 2014 20:02:25 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH] softirq: punt to ksoftirqd if __do_softirq recently looped |
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On 04/11/2014 04:33 PM, David Miller wrote: > From: Rik van Riel <riel@redhat.com> > Date: Thu, 10 Apr 2014 11:57:06 -0400 > >> @@ -330,7 +334,11 @@ void irq_enter(void) >> >> static inline void invoke_softirq(void) >> { >> - if (!force_irqthreads) { >> + /* >> + * If force_irqthreads is set, or if we looped in __do_softirq this >> + * jiffie, punt to ksoftirqd to prevent userland starvation. >> + */ >> + if (!force_irqthreads && this_cpu_read(softirq_looped) != jiffies) { > > If we do this, which I'm not convinced of yet, I think we should use two > jiffies as the cutoff.
I am not fully convinced, either. This patch mostly just illustrates the problem, and gives something that solves Jiri's immediate problem.
It is quite likely that there is a better way to solve the problem of: 1) softirq handling starving out userspace processing, 2) which could be solved by moving the userspace process elsewhere, and 3) shifting softirq processing to ksoftirqd
A working patch seems to be one of the better ways to start a discussion, though.
If anybody has a nicer idea on how to solve the problem, I'd even be willing to implement your idea, and give Jiri another patch to test :)
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