netdev - Re: [PATCH] ucc_geth: Move freeing of TX packets to NAPI context.

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Date:	Mon, 30 Mar 2009 16:34:47 +0800
From:	Li Yang <leoli@...escale.com>
To:	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
Cc:	avorontsov@...mvista.com,
	linuxppc-dev Development <linuxppc-dev@...abs.org>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] ucc_geth: Move freeing of TX packets to NAPI context.

On Thu, Mar 26, 2009 at 1:51 AM, Joakim Tjernlund
<Joakim.Tjernlund@...nsmode.se> wrote:
> Anton Vorontsov <avorontsov@...mvista.com> wrote on 25/03/2009 15:25:40:
>> On Wed, Mar 25, 2009 at 02:30:49PM +0100, Joakim Tjernlund wrote:
>> > >>From 1c2f23b1f37f4818c0fd0217b93eb38ab6564840 Mon Sep 17 00:00:00
> 2001
>> > From: Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
>> > Date: Tue, 24 Mar 2009 10:19:27 +0100
>> > Subject: [PATCH] ucc_geth: Move freeing of TX packets to NAPI context.
>> >  Also increase NAPI weight somewhat.
>> >  This will make the system alot more responsive while
>> >  ping flooding the ucc_geth ethernet interaface.
>>
>> Some time ago I've tried a similar thing for this driver, but during
>> tcp (or udp I don't quite remember) netperf tests I was getting tx
>> watchdog timeouts after ~2-5 minutes of work. I was testing with a
>> gigabit and 100 Mbit link, with 100 Mbit link the issue was not
>> reproducible.
>>
>> Though, I recalling I was doing a bit more than your patch: I was
>> also clearing the TX events in the ucce register before calling
>> ucc_geth_tx, that way I was trying to avoid stale interrupts. That
>> helped to increase an overall performance (not only responsiveness),
>> but as I said my approach didn't pass the tests.
>>
>> I don't really think that your patch may cause this, but can you
>> try netperf w/ this patch applied anyway? And see if it really
>> doesn't cause any issues under stress?
>
> Does the line(in ucc_geth_tx()) look OK to you:
>        if ((bd == ugeth->txBd[txQ]) && (netif_queue_stopped(dev) == 0))
>                        break;
>
> Sure does look fishy to me.

There are two cases when txBd=ConfBd: the BD ring is full or empty.
The condition used here ensures that it is the empty case.  Because in
hard_start_xmit, the queue will be stopped when the BD ring is full.
Maybe some comment is needed here.

- Leo
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