netdev - Re: [PATCH v2 00/46] Clean up RX copybreak and DMA handling

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Message-Id: <20110710.235458.1549578255936886669.davem@davemloft.net>
Date:	Sun, 10 Jul 2011 23:54:58 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mirq-linux@...e.qmqm.pl
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v2 00/46] Clean up RX copybreak and DMA handling

From: Micha┅ Miros┅aw <mirq-linux@...e.qmqm.pl>
Date: Mon, 11 Jul 2011 02:52:46 +0200 (CEST)

>   1. under packet storm and memory pressure NIC keeps generating interrupts
>      (if non-NAPI) and indicating new buffers because it always has free
>      RX buffers --- this only wastes CPU and bus bandwidth transferring
>      data that is going to be immediately discarded;

Actually, this is exactly how I, and others advise people to implement
drivers.  It is the right thing to do.

The worst thing that can happen is to let the RX ring empty of
buffers.  Some cards hang as a result of this, and also it causes head
of line blocking on multiqueue cards, etc.

So the first thing the driver should do is try to allocate a
replacement buffer.

And if that fails, it should give the RX packet right back to the
card, and not pass it up the stack.
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