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From: Tom Lendacky <thomas.lendacky@amd.com>
To: David Miller <davem@davemloft.net>
Cc: <netdev@vger.kernel.org>, <christoffer.dall@linaro.org>
Subject: Re: [PATCH net] amd-xgbe: Use wmb before updating current descriptor count
Date: Fri, 23 Oct 2015 08:35:52 -0500	[thread overview]
Message-ID: <562A37B8.2090108@amd.com> (raw)
In-Reply-To: <20151023.025943.873672852211823864.davem@davemloft.net>

On 10/23/2015 04:59 AM, David Miller wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> Date: Wed, 21 Oct 2015 15:37:05 -0500
>
>> The code currently uses the lightweight dma_wmb barrier before updating
>> the current descriptor count. Under heavy load, the Tx cleanup routine
>> was seeing the updated current descriptor count before the updated
>> descriptor information. As a result, the Tx descriptor was being cleaned
>> up before it was used because it was not "owned" by the hardware yet,
>> resulting in a Tx queue hang.
>>
>> Using the wmb barrier insures that the descriptor is updated before the
>> descriptor counter preventing the Tx queue hang. For extra insurance,
>> the Tx cleanup routine is changed to grab the current decriptor count on
>> entry and uses that initial value in the processing loop rather than
>> trying to chase the current value.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> Tested-by: Christoffer Dall <christoffer.dall@linaro.org>
>
> Applied, thanks.

Hi David,

Can you queue this up for stable?  It is applicable to 4.1 and 4.2.

Thanks,
Tom

>

  reply	other threads:[~2015-10-23 13:35 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-21 20:37 [PATCH net] amd-xgbe: Use wmb before updating current descriptor count Tom Lendacky
2015-10-23  9:59 ` David Miller
2015-10-23 13:35   ` Tom Lendacky [this message]
2015-10-23 14:02     ` David Miller
2015-10-23 16:29 ` Alexander Duyck
2015-10-23 16:57   ` Tom Lendacky
2015-10-24  0:43     ` David Miller

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