Submitter | Eric Dumazet |
---|---|

Date | May 18, 2009, 4:40 p.m. |

Message ID | <4A118F98.60101@cosmosbay.com> |

Download | mbox | patch |

Permalink | /patch/27365/ |

State | Changes Requested |

Delegated to: | David Miller |

Headers | show |

## Comments

On Mon, May 18, 2009 at 06:40:56PM +0200, Eric Dumazet wrote: > Jarek Poplawski a écrit : > > On Fri, May 15, 2009 at 03:49:31PM +0100, Antonio Almeida wrote: > > ... > >> I also note that, for HTB rate configurations over 500Mbit/s on leaf > >> class, when I stop the traffic, in the output of "tc -s -d class ls > >> dev eth1" command, I see that leaf's rate (in bits/s) is growing > >> instead of decreasing (as expected since I've stopped the traffic). > >> Rate in pps is ok and decreases until 0pps. Rate in bits/s increases > >> above 1000Mbit and stays there for a few minutes. After two or three > >> minutes it becomes 0bit. The same happens for it's ancestors (also for > >> root class).Here's tc output of my leaf class for this situation: > >> > >> class htb 1:108 parent 1:10 leaf 108: prio 7 quantum 1514 rate > >> 555000Kbit ceil 555000Kbit burst 70901b/8 mpu 0b overhead 0b cburst > >> 70901b/8 mpu 0b overhead 0b level 0 > >> Sent 120267768144 bytes 242475339 pkt (dropped 62272599, overlimits 0 > >> requeues 0) > >> rate 1074Mbit 0pps backlog 0b 0p requeues 0 > >> lended: 242475339 borrowed: 0 giants: 0 > >> tokens: 8 ctokens: 8 > > > > This looks like a regular bug. I guess it's an overflow in > > gen_estimator(), but I'm not sure there is nothing more. Could you > > try the patch below? (An offset warning when patching 2.6.25 is OK) > > > > Thanks, > > Jarek P. > > --- > > > > net/core/gen_estimator.c | 6 +++++- > > 1 files changed, 5 insertions(+), 1 deletions(-) > > > > diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c > > index 9cc9f95..87f0ced 100644 > > --- a/net/core/gen_estimator.c > > +++ b/net/core/gen_estimator.c > > @@ -127,7 +127,11 @@ static void est_timer(unsigned long arg) > > npackets = e->bstats->packets; > > rate = (nbytes - e->last_bytes)<<(7 - idx); > > e->last_bytes = nbytes; > > - e->avbps += ((long)rate - (long)e->avbps) >> e->ewma_log; > > + if (rate > e->avbps) > > + e->avbps += (rate - e->avbps) >> e->ewma_log; > > + else > > + e->avbps -= (e->avbps - rate) >> e->ewma_log; > > + > > e->rate_est->bps = (e->avbps+0xF)>>5; > > > > rate = (npackets - e->last_packets)<<(12 - idx); > > With a typical estimator "1sec 8sec", ewma_log value is 3 > > At gigabit speeds, we are very close to overflow yes, since > we only have 27 bits available, so 134217728 bytes per second > or 1073741824 bits per second. > > So formula : > e->avbps += ((long)rate - (long)e->avbps) >> e->ewma_log; > is going to overflow. > > One way to avoid the overflow would be to use a smaller estimator, like "500ms 4sec" > > Or use a 64bits rate & avbps, this is needed fo 10Gb speeds I suppose... Yes, I considered this too, but because of an overhead I decided to fix as designed (according to the comment) for now. But probably you are right, and we should go further, so I'm OK with your patch. Jarek P. > > diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c > index 9cc9f95..150e2f5 100644 > --- a/net/core/gen_estimator.c > +++ b/net/core/gen_estimator.c > @@ -86,9 +86,9 @@ struct gen_estimator > spinlock_t *stats_lock; > int ewma_log; > u64 last_bytes; > + u64 avbps; > u32 last_packets; > u32 avpps; > - u32 avbps; > struct rcu_head e_rcu; > struct rb_node node; > }; > @@ -115,6 +115,7 @@ static void est_timer(unsigned long arg) > rcu_read_lock(); > list_for_each_entry_rcu(e, &elist[idx].list, list) { > u64 nbytes; > + u64 brate; > u32 npackets; > u32 rate; > > @@ -125,9 +126,9 @@ static void est_timer(unsigned long arg) > > nbytes = e->bstats->bytes; > npackets = e->bstats->packets; > - rate = (nbytes - e->last_bytes)<<(7 - idx); > + brate = (nbytes - e->last_bytes)<<(7 - idx); > e->last_bytes = nbytes; > - e->avbps += ((long)rate - (long)e->avbps) >> e->ewma_log; > + e->avbps += ((s64)(brate - e->avbps)) >> e->ewma_log; > e->rate_est->bps = (e->avbps+0xF)>>5; > > rate = (npackets - e->last_packets)<<(12 - idx); > -- 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

From: Jarek Poplawski <jarkao2@gmail.com> Date: Mon, 18 May 2009 19:23:49 +0200 > On Mon, May 18, 2009 at 06:40:56PM +0200, Eric Dumazet wrote: >> With a typical estimator "1sec 8sec", ewma_log value is 3 >> >> At gigabit speeds, we are very close to overflow yes, since >> we only have 27 bits available, so 134217728 bytes per second >> or 1073741824 bits per second. >> >> So formula : >> e->avbps += ((long)rate - (long)e->avbps) >> e->ewma_log; >> is going to overflow. >> >> One way to avoid the overflow would be to use a smaller estimator, like "500ms 4sec" >> >> Or use a 64bits rate & avbps, this is needed fo 10Gb speeds I suppose... > > Yes, I considered this too, but because of an overhead I decided to > fix as designed (according to the comment) for now. But probably you > are right, and we should go further, so I'm OK with your patch. I like this patch too, Eric can you submit this formally with proper signoffs etc.? Thanks! -- 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

## Patch

diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c index 9cc9f95..150e2f5 100644 --- a/net/core/gen_estimator.c +++ b/net/core/gen_estimator.c @@ -86,9 +86,9 @@ struct gen_estimator spinlock_t *stats_lock; int ewma_log; u64 last_bytes; + u64 avbps; u32 last_packets; u32 avpps; - u32 avbps; struct rcu_head e_rcu; struct rb_node node; }; @@ -115,6 +115,7 @@ static void est_timer(unsigned long arg) rcu_read_lock(); list_for_each_entry_rcu(e, &elist[idx].list, list) { u64 nbytes; + u64 brate; u32 npackets; u32 rate; @@ -125,9 +126,9 @@ static void est_timer(unsigned long arg) nbytes = e->bstats->bytes; npackets = e->bstats->packets; - rate = (nbytes - e->last_bytes)<<(7 - idx); + brate = (nbytes - e->last_bytes)<<(7 - idx); e->last_bytes = nbytes; - e->avbps += ((long)rate - (long)e->avbps) >> e->ewma_log; + e->avbps += ((s64)(brate - e->avbps)) >> e->ewma_log; e->rate_est->bps = (e->avbps+0xF)>>5; rate = (npackets - e->last_packets)<<(12 - idx);