Messages in this thread | | | Subject | Re: [patch 01/15] Kernel Tracepoints | From | Peter Zijlstra <> | Date | Tue, 15 Jul 2008 15:59:16 +0200 |
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On Tue, 2008-07-15 at 09:25 -0400, Mathieu Desnoyers wrote: > * Peter Zijlstra (peterz@infradead.org) wrote: > > On Wed, 2008-07-09 at 10:59 -0400, Mathieu Desnoyers wrote:
> > > +#define __DO_TRACE(tp, proto, args) \ > > > + do { \ > > > + int i; \ > > > + void **funcs; \ > > > + preempt_disable(); \ > > > + funcs = (tp)->funcs; \ > > > + smp_read_barrier_depends(); \ > > > + if (funcs) { \ > > > + for (i = 0; funcs[i]; i++) { \ > > > > can't you get rid of 'i' and write: > > > > void **func; > > > > preempt_disable(); > > func = (tp)->funcs; > > smp_read_barrier_depends(); > > for (; func; func++) > > ((void (*)(proto))func)(args); > > preempt_enable(); > > > > Yes, I though there would be an optimization to do here, I'll use your > proposal. This code snippet is especially important since it will > generate instructions near every tracepoint side. Saving a few bytes > becomes important. > > Given that (tp)->funcs references an array of function pointers and that > it can be NULL, the if (funcs) test must still be there and we must use > > #define __DO_TRACE(tp, proto, args) \ > do { \ > void *func; \ > \ > preempt_disable(); \ > if ((tp)->funcs) { \ > func = rcu_dereference((tp)->funcs); \ > for (; func; func++) { \ > ((void(*)(proto))(func))(args); \ > } \ > } \ > preempt_enable(); \ > } while (0) > > > The resulting assembly is a bit more dense than my previous > implementation, which is good :
My version also has that if ((tp)->funcs), but its hidden in the for (; func; func++) loop. The only thing your version does is an extra test of tp->funcs but without read depends barrier - not sure if that is ok.
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