[ovs-dev] [loops 6/6] datapath: Detect and suppress flows that are implicated in loops.

Ben Pfaff blp at nicira.com
Tue Aug 3 14:42:30 PDT 2010


On Tue, Aug 03, 2010 at 01:58:51PM -0700, Jesse Gross wrote:
> On Tue, Aug 3, 2010 at 11:15 AM, Ben Pfaff <blp at nicira.com> wrote:
> 
> > +       if (!flow_node) {
> 
> While you're in here, can you put in an unlikely()?

OK, sure.

> +       /* Check whether we've looped too much. */
> > +       loop = &get_cpu_var(dp_loop_counters).counters[!!in_interrupt()];
> > +       if (++loop->count > DP_MAX_LOOPS)
> > +               loop->looping = true;
> 
> 
> This is the extra branch that I was referring to.  We can't eliminate it
> completely but now in the non-loop case it will never be taken so it will be
> no problem for the branch predictor (we could throw in an unlikely()
> though).

Thanks, I added it here too.

> Other than these minor things it looks good.  I tried to think of ways to
> eliminate additional work but didn't really see any.  It should be pretty
> insignificant though.

I didn't see any easy way either.  Thanks again, I pushed this out.




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