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Date: Tue, 16 Jun 2009 15:02:24 -0700 (Pacific Daylight Time)
From: "Brandeburg, Jesse" <jesse.brandeburg@...el.com>
To: Andy Gospodarek <andy@...yhouse.net>
cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
Subject: Re: [PATCH net-next-2.6] ixgbe: fix multi-ring polling [V2]
On Tue, 16 Jun 2009, Andy Gospodarek wrote:
> > > When looking at ixgbe_clean_rxtx_many I noticed two small problems.
> > >
> > > - work_done needs to be cleared before calling ixgbe_clean_rx_irq since
> > > it will exit without cleaning any buffers when work_done is greater
> > > than budget (which could happen pretty often after the first ring is
> > > cleaned). A total count will ensure we still return the correct
> > > number of frames processed.
> >
> > but (not seen in the below patch) the budget is divided by the number of
> > rings on this vector before it is passed to rx_clean, so each ring will
> > always get a chance to clean at least one buffer.
> >
>
> Not by my reading of ixgbe_clean_rx_irq (which could be wrong, but I've
> looked again to be sure). If we have 2 rings that need to be cleaned
> and a budget of 64 passed into ixgbe_clean_rxtx_many, then budget will
> be 32 inside the loop. If the system is busy and there are more than 32
> buffers that need to be cleaned on the first ring ixgbe_clean_rx_irq
> will not break until work_done is 32. When the second ring is polled,
> work_done is already 32 and so is budget. The while loop in
> ixgbe_clean_rx_irq will break immediately and nothing will be cleaned on
> the second ring. Let me know if I'm missing something.
ah, you're right, the second loop will already have work_done set, so it
should be cleared each loop as your patch does.
> > > - napi_complete should only be called if all rings associated with this
> > > napi instance were cleaned completely. It seems wise to stay on the
> > > poll-list if not completely cleaned.
> >
> > that part I agree to.
> >
> > >
> > > This has been compile tested only.
> >
> > we can test it but I think we need a V2, see below...
> >
> > >
> > > Signed-off-by: Andy Gospodarek <andy@...yhouse.net>
> > > ---
> > >
> > > ixgbe_main.c | 11 +++++++----
> > > 1 file changed, 7 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/net/ixgbe/ixgbe_main.c b/drivers/net/ixgbe/ixgbe_main.c
> > > index a551a96..c009642 100644
> > > --- a/drivers/net/ixgbe/ixgbe_main.c
> > > +++ b/drivers/net/ixgbe/ixgbe_main.c
> > > @@ -1362,9 +1362,9 @@ static int ixgbe_clean_rxtx_many(struct napi_struct *napi, int budget)
> > > container_of(napi, struct ixgbe_q_vector, napi);
> > > struct ixgbe_adapter *adapter = q_vector->adapter;
> > > struct ixgbe_ring *ring = NULL;
> > > - int work_done = 0, i;
> > > + int work_done = 0, total_work = 0, i;
> > > long r_idx;
> > > - bool tx_clean_complete = true;
> > > + bool rx_clean_complete = true, tx_clean_complete = true;
> > >
> > > r_idx = find_first_bit(q_vector->txr_idx, adapter->num_tx_queues);
> > > for (i = 0; i < q_vector->txr_count; i++) {
> > > @@ -1384,12 +1384,15 @@ static int ixgbe_clean_rxtx_many(struct napi_struct *napi, int budget)
> > > budget = max(budget, 1);
> > > r_idx = find_first_bit(q_vector->rxr_idx, adapter->num_rx_queues);
> > > for (i = 0; i < q_vector->rxr_count; i++) {
> > > + work_done = 0;
> > > ring = &(adapter->rx_ring[r_idx]);
> > > #ifdef CONFIG_IXGBE_DCA
> > > if (adapter->flags & IXGBE_FLAG_DCA_ENABLED)
> > > ixgbe_update_rx_dca(adapter, ring);
> > > #endif
> > > ixgbe_clean_rx_irq(q_vector, ring, &work_done, budget);
> > > + total_work += work_done;
> > > + rx_clean_complete &= (work_done < budget);
> > > r_idx = find_next_bit(q_vector->rxr_idx, adapter->num_rx_queues,
> > > r_idx + 1);
> > > }
> > > @@ -1397,7 +1400,7 @@ static int ixgbe_clean_rxtx_many(struct napi_struct *napi, int budget)
> > > r_idx = find_first_bit(q_vector->rxr_idx, adapter->num_rx_queues);
> > > ring = &(adapter->rx_ring[r_idx]);
> > > /* If all Rx work done, exit the polling mode */
> > > - if (work_done < budget) {
> > > + if (rx_clean_complete && tx_clean_complete) {
> > > napi_complete(napi);
> > > if (adapter->itr_setting & 1)
> > > ixgbe_set_itr_msix(q_vector);
> > > @@ -1407,7 +1410,7 @@ static int ixgbe_clean_rxtx_many(struct napi_struct *napi, int budget)
> > > return 0;
> > > }
> > >
> > > - return work_done;
> > > + return total_work;
> >
> > I don't think you can return total_work here unless it is always
> > == budget, otherwise NAPI will hang.
> >
> > before the only values that would ever be returned were:
> >
> > 1) napi_complete, return work_done (work_done < budget)
> > 2) return work_done (work_done >= budget)
> >
> > I'm not sure if the > case is even valid in the new napi model, the only
> > one we ever use is the work_done == budget to continue polling.
> >
>
> Adding a check is no problem, but that means we need to save the
> original budget. It would be good to do that to avoid the WARN_ON_ONCE
> in net_rx_action as well, but should we be cheating like that? Here's
> the new patch:
I hope davem can comment on that.
> [PATCH net-next-2.6] ixgbe: fix multi-ring polling V2
I think technically I'm okay with V2, the outstanding questions about what
exactly we should return need to be answered.
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