Message ID | 1309097254.5134.24.camel@mojatatu |
---|---|
State | Superseded, archived |
Delegated to: | David Miller |
Headers | show |
Le dimanche 26 juin 2011 à 10:07 -0400, jamal a écrit : > Got the 10G intel cards installed finally and repeated > the tests on both dummy and Ixgbe. The unfairness was much > higher with 10G than with dummy. The logs contain the results. > > I could send another patch with stats gathering. > The best place seems to be in net/softnet_stat re-using > the fast route entries. > Hi Jamal I would just remove the jiffies break, now we have a 64 packets limit... if (quota >= work || need_resched()) { ... } -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, 2011-06-26 at 17:09 +0200, Eric Dumazet wrote: > I would just remove the jiffies break, now we have a 64 packets limit... > > if (quota >= work || need_resched()) { > ... > } Seems reasonable to do. Some stats (on two different machines at least with dummy) on a system with low # of processes: ~80% of the time - we exit the loop because of packet quota ~1% for both need_resched and jiffy ~19% simply because there were less than quota packets Note: we do use a jiffy check on net_rx_action() but i suspect we never ever hit it. cheers, jamal -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Le dimanche 26 juin 2011 à 11:32 -0400, jamal a écrit : > On Sun, 2011-06-26 at 17:09 +0200, Eric Dumazet wrote: > > > > I would just remove the jiffies break, now we have a 64 packets limit... > > > > if (quota >= work || need_resched()) { > > ... > > } > > Seems reasonable to do. Some stats (on two different machines > at least with dummy) on a system with low # of processes: > ~80% of the time - we exit the loop because of packet quota > ~1% for both need_resched and jiffy > ~19% simply because there were less than quota packets > > Note: we do use a jiffy check on net_rx_action() but i suspect > we never ever hit it. This is because of commit 24f8b2385e03a4f. Prior to this, we could exit very fast from this function, even after receiving a single packet. jiffies break is kind of lazy, IMHO ;) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, 2011-06-26 at 17:53 +0200, Eric Dumazet wrote: > > This is because of commit 24f8b2385e03a4f. > > Prior to this, we could exit very fast from this function, even after > receiving a single packet. > > jiffies break is kind of lazy, IMHO ;) And subjective to the value of Hz. In the case of net_rx_action it seems that we need "something" other than packet budget to get us out of there in extreme case when we loop and none of the netdevs have anything to offer. In the other extreme it would be very unfair to yield because of jiffies when budget is not exhausted and devices have something to offer. One approach could be to deduct their napi weight when they return a 0 for work done. cheers, jamal -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index b4c6809..578269e 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -190,14 +190,18 @@ static inline int qdisc_restart(struct Qdisc *q) void __qdisc_run(struct Qdisc *q) { unsigned long start_time = jiffies; + int quota = 0; + int work = weight_p; while (qdisc_restart(q)) { + quota++; /* - * Postpone processing if - * 1. another process needs the CPU; - * 2. we've been doing it for too long. + * Ordered by possible occurrence: Postpone processing if + * 1. we've exceeded packet quota + * 2. another process needs the CPU; + * 3. we've been doing it for too long. */ - if (need_resched() || jiffies != start_time) { + if (quota >= work || need_resched() || jiffies != start_time) { __netif_schedule(q); break; }
Got the 10G intel cards installed finally and repeated the tests on both dummy and Ixgbe. The unfairness was much higher with 10G than with dummy. The logs contain the results. I could send another patch with stats gathering. The best place seems to be in net/softnet_stat re-using the fast route entries. cheers, jamal commit e7fbab65da4db8d2ef1a61c915dfa8c96c2e0368 Author: Jamal Hadi Salim <jhs@mojatatu.com> Date: Sun Jun 26 09:19:48 2011 -0400 [PATCH] net_sched: fix dequeuer fairness Results on dummy device can be seen in my netconf 2011 slides. These results are for a 10Gige IXGBE intel nic - on another i5 machine, very similar specs to the one used in the netconf2011 results. It turns out - this is a hell lot worse than dummy and so this patch is even more beneficial for 10G. Test setup: ---------- System under test sending packets out. Additional box connected directly dropping packets. Installed prio qdisc on the eth device and default netdev default length of 1000 used as is. The 3 prio bands each were set to 100 (didnt factor in the results). 5 packet runs were made and the middle 3 picked. results ------- The "cpu" column indicates the which cpu the sample was taken on, The "Pkt runx" carries the number of packets a cpu dequeued when forced to be in the "dequeuer" role. The "avg" for each run is the number of times each cpu should be a "dequeuer" if the system was fair. 3.0-rc4 (plain) cpu Pkt run1 Pkt run2 Pkt run3 ================================================ cpu0 21853354 21598183 22199900 cpu1 431058 473476 393159 cpu2 481975 477529 458466 cpu3 23261406 23412299 22894315 avg 11506948 11490372 11486460 3.0-rc4 with patch and default weight 64 cpu Pkt run1 Pkt run2 Pkt run3 ================================================ cpu0 13205312 13109359 13132333 cpu1 10189914 10159127 10122270 cpu2 10213871 10124367 10168722 cpu3 13165760 13164767 13096705 avg 11693714 11639405 11630008 As you can see the system is still not perfect but is a lot better than what it was before... At the moment we use the old backlog weight, weight_p which is 64 packets. It seems to be reasonably fine with that value. The system could be made more fair if we reduce the weight_p (as per my presentation), but we are going to affect the shared backlog weight. Unless deemed necessary, I think the default value is fine. If not we could add yet another knob. Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>