On Mon, Oct 19, 2015 at 8:01 AM, Florian Westphal <f...@strlen.de> wrote: > Andrew Shewmaker <ags...@gmail.com> wrote: >> If alpha is strictly reduced by alpha >> dctcp_shift_g and if alpha is less >> than 1 << dctcp_shift_g, then alpha may never reach zero. For example, >> given shift_g=4 and alpha=15, alpha >> dctcp_shift_g yields 0 and alpha >> remains 15. The effect isn't noticeable in this case below cwnd=137, but >> could gradually drive uncongested flows with leftover alpha down to >> cwnd=137. A larger dctcp_shift_g would have a greater effect. >> >> This change causes alpha=15 to drop to 0 instead of being decrementing by 1 >> as it would when alpha=16. However, it requires one less conditional to >> implement since it doesn't have to guard against subtracting 1 from 0U. A >> decay of 15 is not unreasonable since an equal or greater amount occurs at >> alpha >= 240. >> >> Signed-off-by: Andrew G. Shewmaker <ags...@gmail.com> > > Acked-by: Florian Westphal <f...@strlen.de> > > [ cwnd=137 is quite large so I don't think its important enough for > -stable ].
If my math is correct (please double check it), then my patch will make a difference in scenarios such as: data center: ~20+ Gbps and 500 microsecond RTT 137 * 9000 * 8 / (500 * pow(10, -6)) / pow(10, 9) = 19.728 Gbps [pkt / W] * [bits / pkt] * [W / sec] regional: ~33+ Mbps and 50 millisecond RTT 137 * 1500 * 8 / (50 * pow(10, -3)) / pow(10, 6) = 32.88 Mbps international: ~11+ Mbps and 150 millisecond RTT 137 * 1500 * 8 / (150 * pow(10, -3)) / pow(10, 6) = 10.96 Mbps Even if the broader internet does not ever configure ECN appropriately for use with DCTCP, I care about the latter two cases because I'm using an RTT-based congestion ratio in the same way as DCTCP uses its ECN-based congestion ratio. A tech report describing use of RTTs in this way, with some preliminary Mininet results, is available: https://www.soe.ucsc.edu/research/technical-reports/UCSC-SOE-15-20 I plan on submitting some RFC patches to DCTCP based on my prototype soon. -- Andrew Shewmaker -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
