netdev - Re: am335x: cpsw: phy ignores max-speed setting

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Date:	Thu, 06 Nov 2014 09:28:23 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dave Taht <dave.taht@...il.com>
Cc:	Yegor Yefremov <yegorslists@...glemail.com>,
	netdev <netdev@...r.kernel.org>,
	"N, Mugunthan V" <mugunthanvnm@...com>, mpa@...gutronix.de,
	lsorense@...lub.uwaterloo.ca, Daniel Mack <zonque@...il.com>
Subject: Re: am335x: cpsw: phy ignores max-speed setting

On Thu, 2014-11-06 at 08:51 -0800, Dave Taht wrote:
> ooh! ooh! I have a BQL enablement patch for the cpsw that I have no
> means of testing against multiple phys. Could
> you give the attached very small patch a shot along the way?
> 
> The results I get on the beaglebone vs netperf-wrapper are pretty
> spectacular - huge increase in throughput, big reduction in
> latency.

Please send this patch inline, so that we can comment, and start a new
thread.

@@ -1375,9 +1380,11 @@ static netdev_tx_t cpsw_ndo_start_xmit(struct sk_buff *skb,
                skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
 
        skb_tx_timestamp(skb);
-
+       len = max(skb->len, CPSW_MIN_PACKET_SIZE);
+       netdev_sent_queue(ndev,len);
        ret = cpsw_tx_packet_submit(ndev, priv, skb);
        if (unlikely(ret != 0)) {
+               netdev_completed_queue(ndev,1,len);
<<you can not do that, its racy with other netdev_completed_queue() calls from TX completion >>
                cpsw_err(priv, tx_err, "desc submit failed\n");
                goto fail;
        }


You need to call netdev_sent_queue(ndev, len); at the correct place,
because we can not 'undo' it.



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