netdev - Re: Regression in net-2.6.24?

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Message-Id: <20071012.013923.72710726.davem@davemloft.net>
Date:	Fri, 12 Oct 2007 01:39:23 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mchan@...adcom.com
Cc:	shemminger@...ux-foundation.org, takano@...-inc.co.jp,
	netdev@...r.kernel.org, ilpo.jarvinen@...sinki.fi
Subject: Re: Regression in net-2.6.24?

From: "Michael Chan" <mchan@...adcom.com>
Date: Fri, 12 Oct 2007 01:54:13 -0700

> On Thu, 2007-10-11 at 19:40 -0700, David Miller wrote:
> > Hmmm, the old code didn't do that and seemingly has the same
> > problem.  Also, if you look at the before-patch code and think
> > about what it does if we ->poll() multiple times for a single
> > interrupt the side-effects are essentially the same.
> > 
> 
> No, the old code before tonight's patch did this:
> 
> if (tp->tg3_flags & TG3_FLAG_TAGGED_STATUS) {
> 	tp->last_tag = sblk->status_tag;
> 	rmb();
> }
> 
> before checking for more work.  The rmb() is there to make sure that the
> status tag is read and stored before we check for more work.

No I understand, thanks!

> [TG3]: Refine napi poll loop.
> 
> Need to read and store sblk->status_tag before checking for more work.
> The status tag is later written back to the hardware when enabling
> interrupts to acknowledge how much work has been processed.  If the
> order is reversed, we can end up acknowledging work we haven't
> processed.
> 
> When we detect tx error, it is more correct to return the rx
> work_done so far instead of 0.
> 
> Signed-off-by: Michael Chan <mchan@...adcom.com>

I'll apply this, thanks a lot!
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