On 02/27/2014 02:31 PM, Eric Dumazet wrote:
> On Thu, 2014-02-27 at 13:51 -0800, Ben Greear wrote:
>
>> That said, the code below appears to work, even if it is
>> not as efficient as it might be?
>>
>> if (msdu_chaining) {
>> struct sk_buff *next = msdu_head->next;
>> struct sk_buff *to_free = next;
>> int space;
>> static int do_once = 1;
>> msdu_head->next = NULL;
>>
>> if (unlikely(do_once)) {
>> ath10k_warn("htt rx msdu_chaining detected %d\n",
>> msdu_chaining);
>> do_once = 0;
>> }
>>
>> while (next) {
>> space = next->len - skb_tailroom(msdu_head);
>>
>> if ((space > 0) &&
>> (pskb_expand_head(msdu_head, 0, space, GFP_ATOMIC) < 0)) {
>> /* TODO: bump some rx-oom error stat */
>> goto outside_continue;
>> }
>> skb_copy_from_linear_data(next, skb_put(msdu_head, next->len),
>> next->len);
>> next = next->next;
>> }
>
> Yep, this is very inefficient , you might copy data very often in
> pskb_expand_head(), then in skb_copy_from_linear_data()
Based on the code above, do you think skb_try_coalesce() is
the best option for this logic?
> Also, if total length is big, you end up doing high order allocations,
> since you generate a linear skb. This might fail under memory pressure.
>
> What is the maximal skb->len of resulting skb ?
According to the page below, msdu are limited to 7935 total. In my testing, I have seen a maximum
of 2 chained skbs (3 total). I do not know the average total combined skb size...but since it
has upper bound of 8k, perhaps that doesn't matter so much?
http://ergodicthoughts.blogspot.com/2012/02/difference-between-mpdu-msdu-ampdu-and.html
Thanks,
Ben
--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc http://www.candelatech.com
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