Messages in this thread | | | Subject | Re: [PATCH v2 net-next] softirq: reduce latencies | From | Eric Dumazet <> | Date | Fri, 04 Jan 2013 00:23:06 -0800 |
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On Fri, 2013-01-04 at 00:15 -0800, Joe Perches wrote: > On Thu, 2013-01-03 at 23:49 -0800, Eric Dumazet wrote: > > In various network workloads, __do_softirq() latencies can be up > > to 20 ms if HZ=1000, and 200 ms if HZ=100. > > This patch changes the fallback to ksoftirqd condition to : > > - A time limit of 2 ms. > > [] > > diff --git a/kernel/softirq.c b/kernel/softirq.c > [] > > +#define MAX_SOFTIRQ_TIME max(1, (2*HZ/1000)) > > And if HZ is 10000? >
Then its OK. 2*10000/1000 -> 20 ticks -> 2 ms
> > asmlinkage void __do_softirq(void) > > { > [] > > + unsigned long end = jiffies + MAX_SOFTIRQ_TIME; > > Perhaps MAX_SOFTIRQ_TIME should be > > #define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) > > though it would be nicer if it were a compile time constant.
If you send a patch to convert msecs_to_jiffies() to an inline function when HZ = 1000, I will gladly use it instead of (2*HZ/1000)
Right now, max(1, msecs_to_jiffies(2)) uses way too many instructions, while it should be the constant 2, known at compile time.
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