Hi Luiz,
On Thu, 2011-08-18 at 03:49 -0400, Luiz Augusto von Dentz wrote:
> Hi Peter,
>
> On Thu, Aug 18, 2011 at 3:37 AM, Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote:
> > When assigning tx quotas for multiple connections, bump fractional
> > amounts to the next higher integer. This can reduce the number of
> > iterations through the tx scheduler. For example, if 5 avail acl
> > buffers are to be used by 3 transmitting connections, the current
> > scheduler will produce quotas of 1, 1, 1, 1, 1. This
> > optimization will instead produce quotas of 2, 2, 1 (ie., 2 less
> > iterations of the tx scheduler).
> >
> > Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
... <snip> ...
> Nice catch, actually after seeing your patch I realize one of my
> patches is wrong in assuming an HCI Channel can only be scheduled once
> per tx_task, but I guess with your changes we can probably assume so,
> right?
Thanks. Yes, in the current scheduler a connection can be scheduled
multiple times per tasklet run.
For example, supposed that acl_cnt == 3 and 2 connections have packets
in their queue. Let's assume for the sake of simplicity that no
connections currently have unacked packets (c->sent == 0). Then (with
the current scheduler),
1st iteration: conn list walked => conn A found (equal unacked)
quote = 3/2 => 1 for conn A
conn A now has 1 unacked packet (after send)
2nd iteration: conn list walked => conn B found (lowest unacked)
quote = 2/2 => 1 for conn B
conn B now has 1 unacked packet (after send)
3rd iteration: conn list walked => conn A found (equal unacked)
quote = 1/2 => 1 for conn A
conn A now has 2 unacked packets (after send)
With the proposed change, only 2 iterations occur:
1st iteration: conn list walked => conn A found (equal unacked)
quote = 3/2 => 2 for conn A
conn A now has 2 unacked packets (after send)
2nd iteration: conn list walked => conn B found (lowest unacked)
quote = 1/2 => 1 for conn B
conn B now has 1 unacked packet (after send)
However, even with this change it may be that connections are scheduled
multiple times per tasklet. This can happen if a connection still has
equal or fewer unacked packets even after spending it's quota.
But I didn't see in your proposal where you assume that an HCI channel
can only be scheduled once (or at least where it breaks down if true).
Regards,
Peter Hurley
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