Re: [PATCH v6] mac80211: Remove control.sta from struct ieee80211_tx_info and restructure tx-path

[Arik Nemtsov <arik@xxxxxxxxxx>]

On Thu, Jul 26, 2012 at 7:31 PM, Thomas Huehn
<thomas@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hi Johannes,
>
> Johannes Berg schrieb:
>
>>>
>>> /home/johannes/sys/wireless/drivers/net/wireless/ti/wlcore/tx.c: In
>>> function ‘wl1271_skb_queue_head’:
>>> /home/johannes/sys/wireless/drivers/net/wireless/ti/wlcore/tx.c:622:48:
>>> warning: ‘hlid’ may be used uninitialized in this function
>>> [-Wuninitialized]
>>
>> Those changes make no sense anyway -- you should be able to pass the
>> station pointer through if it previously used info->control.sta, instead
>> of doing an (expensive) lookup.
>
>
> This is the call path
>
> in main.c ... INIT_WORK(&wl->tx_work, wl1271_tx_work);
>  jumps to tx.c...wl1271_tx_work(struct work_struct *work)
>   calls wl1271_tx_work(struct work_struct *work)
>    calls wlcore_tx_work_locked(struct wl1271 *wl)
>     calls wl1271_skb_queue_head()
>      calls wl12xx_tx_get_hlid()
>       calls wl12xx_tx_get_hlid_ap() .... where sta is needed.
>
> But I could not find any point in the call path where I could grab the
> sta pointer and pass it through. I will move the rcu into
> wl12xx_tx_get_hlid_ap(), but I do not see any cheaper way here as using rcu.

I agree with Johannes. The find_sta() in the Tx path is unacceptable.

A relatively simple change here would be to put the sta pointer in the
portion of the struct reserved for rate control during op_tx(). wlcore
doesn't use software rate control anyway.
This would avoid from changing the code too much.
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