[Cake] quick patch for split_gso

[Dave Taht]

so, I went and tested that patch. Turned out len was signed... I'd put
it in the wrong place... and the very act of doing that test at all
permutes the result.

cake unshaped at 1gig, always splitting, ends up with a bql value of
about 42,000, full throughput, e.g.

if (skb_is_gso(skb)) {

...

                           avg       median          # data pts
 Ping (ms) ICMP :         0.80         0.77 ms              341
 TCP upload avg :       235.40       235.39 Mbits/s         301
 TCP upload sum :       941.61       941.55 Mbits/s         301
 TCP upload::1  :       235.36       235.39 Mbits/s         290
 TCP upload::2  :       235.46       235.39 Mbits/s         291
 TCP upload::3  :       235.38       235.45 Mbits/s         275
 TCP upload::4  :       235.41       235.44 Mbits/s         278

conditionally splitting, either never or always, gives me bql of: 140852

        if (skb_is_gso(skb) && len >= q->split_gso) {

                           avg       median          # data pts
 Ping (ms) ICMP :         1.64         1.71 ms              347
 TCP upload avg :       235.40       235.38 Mbits/s         301
 TCP upload sum :       941.59       941.52 Mbits/s         301
 TCP upload::1  :       235.35       235.44 Mbits/s         280
 TCP upload::2  :       235.40       235.39 Mbits/s         276
 TCP upload::3  :       235.47       235.43 Mbits/s         276
 TCP upload::4  :       235.37       235.45 Mbits/s         282

the cache line miss can't possibly have cost that much. (?) Guess I
have to go check the range of len.

I WANT MY 800usec back!

PS For giggles, I accidentally ended up using pfifo_fast for one run.
I thought I'd broke something.

Summary of tcp_nup test run 'split_gso_test_again_len_512000_bql_auto'
(at 2018-07-25 20:51:10.533339):

                           avg       median          # data pts
 Ping (ms) ICMP :         3.32         3.59 ms              347
 TCP upload avg :       235.38       235.38 Mbits/s         301
 TCP upload sum :       941.52       941.54 Mbits/s         301
 TCP upload::1  :       152.48       150.93 Mbits/s         281
 TCP upload::2  :       152.54       150.35 Mbits/s         286
 TCP upload::3  :       483.96       491.12 Mbits/s         284
 TCP upload::4  :       152.54       150.49 Mbits/s         284
On Tue, Jul 24, 2018 at 10:01 PM Dave Taht <dave.taht at gmail.com> wrote:
>
> Ah... 1gbit, BQL at a sane size, 750 usec RTT. I guess I have to go
> compile this patch now.....
>
>
> --
>
> Dave Täht
> CEO, TekLibre, LLC
> http://www.teklibre.com
> Tel: 1-669-226-2619



-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619
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