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

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Date:	Mon, 18 Feb 2013 14:10:55 -0600
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Rafał Miłecki <zajec5@...il.com>
CC:	linville@...driver.com, linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org, Bastian Bittorf <bittorf@...ebottle.com>,
	Stable <stable@...r.kernel.org>
Subject: Re: [PATCH] b43: Increase number of RX DMA slots

On 02/18/2013 10:18 AM, Rafał Miłecki wrote:
> 2013/2/18 Larry Finger <Larry.Finger@...inger.net>:
>> 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.
>
> So probably ideal solution is to use 128 *and* fix the driver's
> failing on overflow ;)
>
> Did you try it on some old device? Just for sure firmware&DMA will
> handle it correctly.

I tested on BCM4318 (which is pretty old), and two different BCM4312 (14e4:4315) 
units. I think the firmware and DMA can handle it. After all, all the TX rings 
have 256 slots. There is, however, a question of the memory. TX only acquires 
the buffers when needed, but RX has to get them in advance, thus 256 slots there 
will waste a lot of memory.

I agree that there be two patches, depending on Bastian's testing. The slot size 
change can be backported to stable.

Larry

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