Re: [net-next 03/10] ixgbe: Drop the TX work limit and instead just leave it to budget

On 08/22/2011 09:46 AM, Ben Hutchings wrote:

On Mon, 2011-08-22 at 09:30 -0700, Alexander Duyck wrote:

quoted

On 08/21/2011 07:01 AM, Ben Hutchings wrote:

quoted

On Sun, 2011-08-21 at 00:29 -0700, Jeff Kirsher wrote:

quoted

From: Alexander Duyck<redacted>

This change makes it so that the TX work limit is now obsolete.  Instead of
using it we can instead rely on the NAPI budget for the number of packets
we should clean per interrupt.  The advantage to this approach is that it
results in a much more balanced work flow since the same number of RX and
TX packets should be cleaned per interrupts.

[...]

This seems kind of sensible, but it's not how Dave has been recommending
people to account for TX work in NAPI.

Ben.

I wasn't aware there was a recommended approach.  Could you tell me more
about it?

If a whole TX ring is cleaned then consider the budget spent; otherwise
don't count it.

Ben.

The only problem I was seeing with that was that in certain cases it seemed like the TX cleanup could consume enough CPU time to cause pretty significant delays in processing the RX cleanup.  This in turn was causing single queue bi-directional routing tests to come out pretty unbalanced since what seemed to happen is that one CPUs RX work would overwhelm the other CPU with the TX processing resulting in an unbalanced flow that was something like a 60/40 split between the upstream and downstream throughput.

Thanks,

Alex