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    SubjectRe: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs
    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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