Messages in this thread | | | Subject | Re: txqueuelen has wrong units; should be time | From | Eric Dumazet <> | Date | Mon, 28 Feb 2011 14:10:40 +0100 |
| |
Le lundi 28 février 2011 à 13:43 +0200, Jussi Kivilinna a écrit : > Quoting Eric Dumazet <eric.dumazet@gmail.com>: > > > Le dimanche 27 février 2011 à 12:55 +0200, Jussi Kivilinna a écrit : > >> Quoting Albert Cahalan <acahalan@gmail.com>: > >> > >> > On Sun, Feb 27, 2011 at 2:54 AM, Eric Dumazet > >> <eric.dumazet@gmail.com> wrote: > >> >> Le dimanche 27 février 2011 à 08:02 +0100, Mikael Abrahamsson a écrit : > >> >>> On Sun, 27 Feb 2011, Albert Cahalan wrote: > >> >>> > >> >>> > Nanoseconds seems fine; it's unlikely you'd ever want > >> >>> > more than 4.2 seconds (32-bit unsigned) of queue. > >> > ... > >> >> Problem is some machines have slow High Resolution timing services. > >> >> > >> >> _If_ we have a time limit, it will probably use the low resolution (aka > >> >> jiffies), unless high resolution services are cheap. > >> > > >> > As long as that is totally internal to the kernel and never > >> > getting exposed by some API for setting the amount, sure. > >> > > >> >> I was thinking not having an absolute hard limit, but an EWMA based one. > >> > > >> > The whole point is to prevent stale packets, especially to prevent > >> > them from messing with TCP, so I really don't think so. I suppose > >> > you do get this to some extent via early drop. > >> > >> I made simple hack on sch_fifo with per packet time limits > >> (attachment) this weekend and have been doing limited testing on > >> wireless link. I think hardlimit is fine, it's simple and does > >> somewhat same as what packet(-hard)limited buffer does, drops packets > >> when buffer is 'full'. My hack checks for timed out packets on > >> enqueue, might be wrong approach (on other hand might allow some more > >> burstiness). > >> > > > > > > Qdisc should return to caller a good indication packet is queued or > > dropped at enqueue() time... not later (aka : never) > > > > Accepting a packet at t0, and dropping it later at t0+limit without > > giving any indication to caller is a problem. > > > > This is why I suggested using an EWMA plus a probabilist drop or > > congestion indication (NET_XMIT_CN) to caller at enqueue() time. > > > > The absolute time limit you are trying to implement should be checked at > > dequeue time, to cope with enqueue bursts or pauses on wire. > > > > Would it be better to implement this as generic feature instead of > qdisc specific? Have qdisc_enqueue_root do ewma check:
Problem is you can have several virtual queues in a qdisc.
For example, pfifo_fast has 3 bands. You could have a global ewma with high values, but you still want to let a high priority packet going through...
-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |