On 2016-03-03 15:54, Johannes Berg wrote: > On Wed, 2016-02-24 at 10:28 +0100, Felix Fietkau wrote: >> >> + /* >> + * HT A-MPDU limits maximum MPDU size to 4095 bytes. Since aggregation >> + * sessions are started/stopped without txq flush, use the limit here >> + * to avoid having to de-aggregate later. >> + */ >> + if (skb->len + head->len > 4095 && >> + !sta->sta.vht_cap.vht_supported) >> + goto out; > > I'm not entirely happy with this. You're silently assuming that when > VHT is supported, HT MCSes will never be used. > > This is (I think) true for minstrel_ht, but at the very least you > should also document it along with the max_rc_amsdu_len then, which btw > I was going to reword to: > > + * @IEEE80211_HW_TX_AMSDU: Hardware (or driver) supports software aggregated > + * A-MSDU frames. Requires software tx queueing and fast-xmit support. > + * When not using minstrel/minstrel_ht rate control, the driver needs to > + * limit the maximum A-MSDU size based on the current tx rate by setting > + * max_rc_amsdu_len in struct ieee80211_sta to avoid mac80211 building > + * A-MSDUs that require too much airtime (are too long for a TXOP.) > > > All that said, I'm not sure how much value there really is in > aggregating that much? I'd think the value of A-MSDU really is more for > lots of small frames like TCP ACKs, since the PER goes up exponentially > with the BER for A-MSDU (unlike A-MPDU.) For my own uses, I'd be perfectly fine with limiting A-MSDU size to HT limits even when using VHT - in fact I did that in an early RFC patch. I mainly relaxed the limit for VHT based on Emmanuel's feedback. I also have doubts about the value of A-MSDU size beyond 4095 bytes.
Just let me know which way you'd like it, and I'll send v3 accordingly. - Felix -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
