Re: [PATCH net-next] sch_netem: faster rb tree removal

On 9/24/17 11:27 PM, Eric Dumazet wrote:

On Sun, 2017-09-24 at 20:05 -0600, David Ahern wrote:

quoted

On 9/24/17 7:57 PM, David Ahern wrote:

quoted

quoted

Hi Eric:

I'm guessing the cost is in the rb_first and rb_next computations. Did
you consider something like this:

        struct rb_root *root
        struct rb_node **p = &root->rb_node;

        while (*p != NULL) {
                struct foobar *fb;

                fb = container_of(*p, struct foobar, rb_node);
                // fb processing

		  rb_erase(&nh->rb_node, root);

quoted

                p = &root->rb_node;
        }

Oops, dropped the rb_erase in my consolidating the code to this snippet.

Hi David

This gives about same numbers than method_1

I tried with 10^7 skbs in the tree :

Your suggestion takes 66ns per skb, while the one I chose takes 37ns per
skb.

Thanks for the test.

I made a simple program this morning and ran it under perf. With the
above suggestion the rb_erase has a high cost because it always deletes
the root node. Your method 1 has a high cost on rb_first which is
expected given its definition and it is run on each removal. Both
options increase in time with the number of entries in the tree.

Your method 2 is fairly constant from 10,000 entries to 10M entries
which makes sense: a one time cost at finding rb_first and then always
removing a bottom node so rb_erase is light.

As for the change:

Acked-by: David Ahern <redacted>