Messages in this thread | | | Date | Thu, 18 Jun 2020 10:32:06 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs |
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On Thu, Jun 18, 2020 at 07:25:04PM +0200, Uladzislau Rezki wrote: > > > + // Handle two first channels. > > > + for (i = 0; i < FREE_N_CHANNELS; i++) { > > > + for (; bkvhead[i]; bkvhead[i] = bnext) { > > > + bnext = bkvhead[i]->next; > > > + debug_rcu_bhead_unqueue(bkvhead[i]); > > > + > > > + rcu_lock_acquire(&rcu_callback_map); > > > + if (i == 0) { // kmalloc() / kfree(). > > > + trace_rcu_invoke_kfree_bulk_callback( > > > + rcu_state.name, bkvhead[i]->nr_records, > > > + bkvhead[i]->records); > > > + > > > + kfree_bulk(bkvhead[i]->nr_records, > > > + bkvhead[i]->records); > > > + } else { // vmalloc() / vfree(). > > > + for (j = 0; j < bkvhead[i]->nr_records; j++) { > > > + trace_rcu_invoke_kfree_callback( > > > + rcu_state.name, > > > + bkvhead[i]->records[j], 0); > > > + > > > + vfree(bkvhead[i]->records[j]); > > > + } > > > + } > > > + rcu_lock_release(&rcu_callback_map); > > > > Not an emergency, but did you look into replacing this "if" statement > > with an array of pointers to functions implementing the legs of the > > "if" statement? If nothing else, this would greatly reduced indentation. > > > > > > I am taking this as is, but if you have not already done so, could you > > please look into this for a follow-up patch? > > > I do not think it makes sense, because it would require to check each > pointer in the array, what can lead to many branching, i.e. "if-else" > instructions.
Mightn't the compiler simply unroll the outer loop? Then the first unrolled iteration of that loop would contain the then-clause and the second unrolled iteration would contain the else-clause. At that point, there would be no checking, just direct calls.
Or am I missing something?
> Paul, thank you to take it in!
Thank you for persisting!
Thanx, Paul
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