netdev - Re: [PATCH net-next 2/2] bnx2x: use the default NAPI weight

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Date:	Tue, 05 Mar 2013 23:03:18 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, eilong@...adcom.com
Subject: Re: [PATCH net-next 2/2] bnx2x: use the default NAPI weight

On Tue, 2013-03-05 at 23:37 -0500, David Miller wrote:

> Thanks for the explanation.
> 
> Since you haven't completely resolved the issues you were running into
> I'll target this to net-next for now.

Thanks David

An other issue is the spin_trylock() attempted in net_tx_action()

It seems we can miss a qdisc_run(), and have to wait the following
NET_TX softirq(s) to send more data. NET_RX being interleaved, we can
have to wait a long time (not mentioning other softirq handlers like
RCU ...)

I might be too tired right now, but cant see the reason of the trylock.

qdisc lock is already BH safe, so we should do a spinlock

I'll test the following patch tomorrow :

 net/core/dev.c |   21 +++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index a06a7a5..d5d4573 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3201,22 +3201,11 @@ static void net_tx_action(struct softirq_action *h)
 			head = head->next_sched;
 
 			root_lock = qdisc_lock(q);
-			if (spin_trylock(root_lock)) {
-				smp_mb__before_clear_bit();
-				clear_bit(__QDISC_STATE_SCHED,
-					  &q->state);
-				qdisc_run(q);
-				spin_unlock(root_lock);
-			} else {
-				if (!test_bit(__QDISC_STATE_DEACTIVATED,
-					      &q->state)) {
-					__netif_reschedule(q);
-				} else {
-					smp_mb__before_clear_bit();
-					clear_bit(__QDISC_STATE_SCHED,
-						  &q->state);
-				}
-			}
+			spin_lock(root_lock);
+			smp_mb__before_clear_bit();
+			clear_bit(__QDISC_STATE_SCHED, &q->state);
+			qdisc_run(q);
+			spin_unlock(root_lock);
 		}
 	}
 }


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