Message-ID: <5671CDBD.5060006@codeaurora.org> (sfid-20151216_214736_598569_5ED012D4)
Date: Wed, 16 Dec 2015 12:46:53 -0800
From: Peter Oh <poh@codeaurora.org>
MIME-Version: 1.0
To: Felix Fietkau <nbd@openwrt.org>, Peter Oh <poh@qca.qualcomm.com>,
	ath10k@lists.infradead.org
CC: linux-wireless@vger.kernel.org
Subject: Re: [PATCH] ath10k: add modparam 'hw_csum' to make HW checksum configurable
References: <1450290051-15593-1-git-send-email-poh@qca.qualcomm.com> <5671AD10.70004@openwrt.org> <5671C99A.703@codeaurora.org> <5671CAF5.6010606@openwrt.org>
In-Reply-To: <5671CAF5.6010606@openwrt.org>
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Sender: linux-wireless-owner@vger.kernel.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