Re: [PATCH] ath10k: add modparam 'hw_csum' to make HW checksum configurable

[Peter Oh <poh@codeaurora.org>]

On 12/16/2015 12:35 PM, Felix Fietkau wrote:
> On 2015-12-16 21:29, Peter Oh wrote:
>> On 12/16/2015 10:27 AM, Felix Fietkau wrote:
>>> On 2015-12-16 19:20, Peter Oh wrote:
>>>> Some hardwares such as QCA988X and QCA99X0 doesn't have
>>>> capability of checksum offload when frame formats are not
>>>> suitable for it such as Mesh frame.
>>>> Hence add a module parameter, hw_csum, to make checksum offload
>>>> configurable during module registration time.
>>>>
>>>> Signed-off-by: Peter Oh <poh@qca.qualcomm.com>
>>> How about instead of inventing yet another crappy module parameter, you
>>> call skb_checksum_help() in the driver in cases where the hardware is
>>> unable to offload the checksum calculation.
>>>
>>> That way the user has to worry about less driver specific hackery ;)
>> That will be good option for hardware not supporting HW checksum, but I
>> mind that using the function will add more workload per every packet on
>> critical data path when HW supports checksum resulting in throughput down.
> I didn't mean calling it for every single frame in the data path.
> What I'm suggesting is calling it selectively only for mesh frames, or
> any other frames that the hardware cannot offload, and leaving the rest
> for the hardware to process.
>
> There should be no performance difference between disabling checksum
> offload and calling skb_checksum_help from the driver.
To call it selectively for Mesh frame or interface, we need to add it on 
mac80211 layer such as ieee80211_build_hdr() since driver layer does not 
care the interface type in data path.
In that case it will also introduce throughput degrade to HW that 
supports HW checksum for Mesh.
> - Felix
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Thanks,
Peter