Re: [PATCH v2 1/4] mac80211: Rearrange ieee80211_tx_info to make room for tx_time_est

[Ben Greear <greearb@candelatech.com>]

On 10/18/2019 05:35 AM, Johannes Berg wrote:
> On Fri, 2019-10-18 at 12:15 +0200, Toke Høiland-Jørgensen wrote:
>> Kan Yan <kyan@google.com> writes:
>>
>>> The "tx_time_est" field, shared by control and status, is not able to
>>> survive until the skb returns to the mac80211 layer in some
>>> architectures. The same space is defined as driver_data and some
>>> wireless drivers use it for other purposes, as the cb in the sk_buff
>>> is free to be used by any layer.
>>>
>>> In the case of ath10k, the tx_time_est get clobbered by
>>> struct ath10k_skb_cb {
>>>         dma_addr_t paddr;
>>>         u8 flags;
>>>         u8 eid;
>>>         u16 msdu_id;
>>>         u16 airtime_est;
>>>         struct ieee80211_vif *vif;
>>>         struct ieee80211_txq *txq;
>>> } __packed;
>>
>> Ah, bugger, of course the driver that actually needs this is using the
>> full driver_data space :P
>
> Looks like you could shrink *this* fairly easily though.
>
> E.g. most likely vif == txq->vif unless txq==NULL, so it's down to 22
> bytes plus a bit/flag for knowing whether the pointer is a vif directly
> (if no TXQ) or a TXQ.

And of course you get two bits in every pointer (0x3) and likely the
dma addr too.  Plenty of space!

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com