Re: [PATCH] b43: Increase number of RX DMA slots

From: "Rafał Miłecki" <zajec5@gmail.com>
To: David Laight <David.Laight@aculab.com>
Cc: David Miller <davem@davemloft.net>,
	Larry.Finger@lwfinger.net, linville@tuxdriver.com,
	linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
	bittorf@bluebottle.com, stable@vger.kernel.org
Subject: Re: [PATCH] b43: Increase number of RX DMA slots
Date: Tue, 19 Feb 2013 10:57:54 +0100	[thread overview]
Message-ID: <CACna6rz9qRFT_YXJN961=LqzQmhaTPbq+_2UG_LoV7hVgQ7gDA@mail.gmail.com> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B7152@saturn3.aculab.com>

2013/2/19 David Laight <David.Laight@aculab.com>:
>> > Bastian Bittorf reported that some of the silent freezes on a Linksys WRT54G
>> > were due to overflow of the RX DMA ring buffer, which was created with 64
>> > slots. That finding reminded me that I was seeing similar crashed on a netbook,
>> > which also has a relatively slow processor. After increasing the number of
>> > slots to 128, runs on the netbook that previously failed now worked; however,
>> > I found that 109 slots had been used in one test. For that reason, the number
>> > of slots is being increased to 256.
>
> Surely the driver should work even if all the RX buffers get filled?
> Increasing the number of buffers is just hiding the issue.
> A burst of 300 back to back small packets probably fills the 256 slots.
>
> I realise that dropping frames isn't ideal, and that small numbers
> of buffers can make it impossible to receive long fragmented IP
> messages. but increasing the number of buffers doesn't seem to
> be the best fix for a 'silent freeze'.
>
> It might be that the driver would be more robust if it only ever
> put rx buffers into all but one of the ring slots.

That's what I said ;) I have this on my TODO, but I need to resolve my
issues with ethernet first.

-- 
Rafał