netdev - Re: [PATCH 1/2] ucc_geth: Move freeing of TX packets to NAPI context.

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Date:	Mon, 30 Mar 2009 15:36:21 +0800
From:	Li Yang <leoli@...escale.com>
To:	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
Cc:	avorontsov@...mvista.com, linuxppc-dev@...abs.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] ucc_geth: Move freeing of TX packets to NAPI context.

On Fri, Mar 27, 2009 at 7:52 PM, Joakim Tjernlund
<Joakim.Tjernlund@...nsmode.se> wrote:
> pku.leo@...il.com wrote on 27/03/2009 11:50:09:
>>
>> On Thu, Mar 26, 2009 at 8:54 PM, Joakim Tjernlund
>> <Joakim.Tjernlund@...nsmode.se> wrote:
>> > Also set NAPI weight to 64 as this is a common value.
>> > This will make the system alot more responsive while
>> > ping flooding the ucc_geth ethernet interaface.
>> >
>> > Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
>> > ---
>> >        /* Errors and other events */
>> >        if (ucce & UCCE_OTHER) {
>> >                if (ucce & UCC_GETH_UCCE_BSY)
>> > @@ -3733,7 +3725,7 @@ static int ucc_geth_probe(struct of_device*
> ofdev, const struct of_device_id *ma
>> >        dev->netdev_ops = &ucc_geth_netdev_ops;
>> >        dev->watchdog_timeo = TX_TIMEOUT;
>> >        INIT_WORK(&ugeth->timeout_work, ucc_geth_timeout_work);
>> > -       netif_napi_add(dev, &ugeth->napi, ucc_geth_poll,
> UCC_GETH_DEV_WEIGHT);
>> > +       netif_napi_add(dev, &ugeth->napi, ucc_geth_poll, 64);
>>
>> It doesn't make sense to have larger napi budget than the size of RX
>> BD ring.  You can't have more BDs than RX_BD_RING_LEN in backlog for
>> napi_poll to process.  Increase the RX_BD_RING_LEN if you want to
>> increase UCC_GETH_DEV_WEIGHT.  However please also provide the
>> performance comparison for this kind of change.  Thanks
>
> Bring it up with David Miller. After my initial attempt to just increase
> weight somewhat, he requested that I hardcoded it to 64. Just read the
> whole thread.
> If I don't increase weight somewhat, ping -f -l 3 almost halts the board.
> Logging
> in takes forever. These are my "performance numbers".

Faster response time is surely good.  But it might also mean CPU is
not fully loaded.  IMHO, throughput is a more important factor for
network devices.  When you try to optimize the driver, please also
consider the throughput change.  Thanks.

- Leo
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