[PATCH net-next v2 0/2] sunvnet: Reduce LDC message overhead.

[PATCH net-next v2 0/2] sunvnet: Reduce LDC message overhead.

[Sowmini Varadhan]

This patchset has an updated version of the v1 changes to reduce the
overhead from LDC messages. 

Re-submitting both patches for completeness.

- Send the minimum number of start and stop messages between producer
  and consumer. 
  Changes since v1 to pull out the unused label `again' and the unused
  `retries' variable

- When reading the descriptor rings, don't give up as soon as a dring
  that is not VIO_DESC_READY is found. 
  Changes since v1: the `again' label and retries variable belong to
  this patch.

I understand the Puristic objection to the polling-delay from
patch 2/2, but the practical reality is that when there is
a burst of data, and performance is actually most critical, 
the overhead from hastily sending an LDC stop and then 
processing another LDC start message is far greater than the 
slight penalty of a small delay when the network traffic is light.

Note that I'm separately working on moving the data handling to a
bottom-half or softirq context, where the poll-based delay will be
even less critical.  We could also consider adding a procfs or ethtool
based knob to disable the fudge-factored delay, and avoid the minor
polling penalty.

Sowmini Varadhan (2):
  Avoid sending superfluous LDC messages.
  Re-check for a VIO_DESC_READY data descriptor after short udelay()

 drivers/net/ethernet/sun/sunvnet.c | 87 ++++++++++++++++++++++++++++++++++----
 drivers/net/ethernet/sun/sunvnet.h |  4 ++
 2 files changed, 83 insertions(+), 8 deletions(-)

-- 
1.8.4.2

Re: [PATCH net-next v2 0/2] sunvnet: Reduce LDC message overhead.

[David Miller]

From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Date: Tue, 2 Sep 2014 12:19:36 -0400

> This patchset has an updated version of the v1 changes to reduce the
> overhead from LDC messages. 

Let's hold on these changes until the memory barrier issues brought up
by David is resolved.

Re: [PATCH net-next v2 0/2] sunvnet: Reduce LDC message overhead.

[Sowmini Varadhan]

On (09/04/14 22:37), David Miller wrote:
> 
> From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
> 
> > This patchset has an updated version of the v1 changes to reduce the
> > overhead from LDC messages. 
> 
> Let's hold on these changes until the memory barrier issues brought up
> by David is resolved.

On (09/07/14 16:19), David Miller wrote (in the patch 2/2 thread for this set):
> 
> > So what (if any) is the outstanding question about wmb() at this 
> > point?
> 
> I don't think there is any, thanks.

I'm not sure where we stand with this- do I need to resubmit any/all of 
those two patches?

--Sowmini

Re: [PATCH net-next v2 0/2] sunvnet: Reduce LDC message overhead.

[David L Stevens]

On 09/08/2014 10:38 AM, Sowmini Varadhan wrote:
>
> I'm not sure where we stand with this- do I need to resubmit any/all of 
> those two patches?

Dave,
	FWIW, I think there may be a memory barrier issue (missing rmb()),
which I'll look into and patch separately, if needed, but I don't think it
has anything to do with this patchset.

My original concern about the wmb() placement was wrong, I agree.

							+-DLS

Re: [PATCH net-next v2 0/2] sunvnet: Reduce LDC message overhead.

[Sowmini Varadhan]

Excuse me if I am missing something obvious, but what was the 
verdict on this? Is there any additional clarification/information 
I can provide, if this is being mulled over? 

--Sowmini

On (09/08/14 10:38), Sowmini Varadhan wrote:
> 
> On (09/04/14 22:37), David Miller wrote:
> > 
> > From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
> > 
> > > This patchset has an updated version of the v1 changes to reduce the
> > > overhead from LDC messages. 
> > 
> > Let's hold on these changes until the memory barrier issues brought up
> > by David is resolved.
> 
> On (09/07/14 16:19), David Miller wrote (in the patch 2/2 thread for this set):
> > 
> > > So what (if any) is the outstanding question about wmb() at this 
> > > point?
> > 
> > I don't think there is any, thanks.
> 
> I'm not sure where we stand with this- do I need to resubmit any/all of 
> those two patches?
> 
> --Sowmini

Re: [PATCH net-next v2 0/2] sunvnet: Reduce LDC message overhead.

[David Miller]

From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Date: Wed, 10 Sep 2014 10:04:34 -0400

> Excuse me if I am missing something obvious, but what was the 
> verdict on this? Is there any additional clarification/information 
> I can provide, if this is being mulled over? 

After the memory barrier stuff has been sorted out, the patches
should be submitted again for review.

But I was under the impression that for now we weren't going to
be doing the new udelay() things, which defers patch #2 for now.

Re: [PATCH net-next v2 0/2] sunvnet: Reduce LDC message overhead.

[Sowmini Varadhan]

On (09/10/14 15:25), David Miller wrote:
> 
> After the memory barrier stuff has been sorted out, the patches
> should be submitted again for review.
> 
> But I was under the impression that for now we weren't going to
> be doing the new udelay() things, which defers patch #2 for now.

ah, ok, I didn't realize the ball was in my court- good that I checked.

I'll re-submit a unified diff without the extra-udelay-stuff
as a v3 patch for review tomorrow.

--Sowmini