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

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Date:	Mon, 30 Mar 2009 09:48:01 +0200
From:	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
To:	Li Yang <leoli@...escale.com>
Cc:	avorontsov@...mvista.com, linuxppc-dev@...abs.org,
	netdev@...r.kernel.org, pku.leo@...il.com
Subject: Re: [PATCH 1/2] ucc_geth: Move freeing of TX packets to NAPI context.

pku.leo@...il.com wrote on 30/03/2009 09:36:21:
> 
> 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.

This particular change isn't about performance, it is about not
"bricking" the board during heavy traffic. Next step is to optimize
the driver.

 Jocke
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