On 13-03-21 11:27 AM, Eric Dumazet wrote: > On Thu, 2013-03-21 at 11:03 -0400, Paul Gortmaker wrote: >> [CC'ing stable & Willy - for the older releases not fed by >> http://patchwork.ozlabs.org/bundle/davem/stable/ ] >> >> On Tue, Mar 5, 2013 at 12:15 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote: >>> From: Eric Dumazet <edumazt@xxxxxxxxxx> >>> >>> We should use time_after_eq() to get maximum latency of two ticks, >>> instead of three. >>> >>> Bug added in commit 24f8b2385 (net: increase receive packet quantum) >> >> I'm not sure what applications would notice the extra tick, but 24f8b takes >> us back to 2.6.29. It cherry picks cleanly onto 2.6.34, so it probably also >> does the same for Willy's 2.6.32 longterm too. >> >> Commit is now mainline d114a3338747255518 - v3.9-rc3~36^2~34. > > BQL (Bytes Queue Limit) relies on TX completion being run often, and > Qdisc being serviced often as well. If net_rx_action() hogs the cpu, > net_tx_action() is delayed and NIC can stall. > > I wrote this patch because I was investigating a regression when a > Google application began using BQL enabled kernels. > > About the latency in itself, following commit is way more interesting. > > commit c10d73671ad30f5 (softirq: reduce latencies) > > As without it, I could trigger more than 50ms latencies for the poor > user thread interrupted by softirq processing. That is also reasonably portable back to 2.6.34. And it is more interesting too -- it will be interesting in a preempt_rt context too, once RT moves ahead off the current 3.6 baseline, which still has the old count-limit of 10 vs the new 2ms time limit. RT (3.4 and 3.6 based) currently has this patch from Steven: http://git.kernel.org/cgit/linux/kernel/git/paulg/3.6-rt-patches.git/tree/net-tx-action-avoid-livelock-on-rt.patch Anyway, thanks for the heads up on this commit. Paul. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html