Re: [PATCH net 2/3] bql: Avoid unneeded limit decrement.

[David Miller <davem@davemloft.net>]

From: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
Date: Thu, 31 May 2012 07:25:19 +0900

> When below pattern is observed,
> 
>                                                TIME
>        dql_queued()         dql_completed()     |
>       a) initial state                          |
>                                                 |
>       b) X bytes queued                         V
> 
>       c) Y bytes queued
>                            d) X bytes completed
>       e) Z bytes queued
>                            f) Y bytes completed
> 
> a) dql->limit has already some value and there is no in-flight packet.
> b) X bytes queued.
> c) Y bytes queued and excess limit.
> d) X bytes completed and dql->prev_ovlimit is set and also
>    dql->prev_num_queued is set Y.
> e) Z bytes queued.
> f) Y bytes completed. inprogress and prev_inprogress are true.
> 
> At f), according to the comment, all_prev_completed becomes
> true and limit should be increased. But POSDIFF() ignores
> (completed == dql->prev_num_queued) case, so limit is decreased.
> 
> Signed-off-by: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>

Applied and queued up for -stable.