On Jun 12, Stanislaw Gruszka wrote: > On Wed, Jun 12, 2019 at 02:59:05PM +0200, Stanislaw Gruszka wrote: > > > > If max RX AMSDU size is 3839B I do not see reason why we allocate > > > > MT_SG_MAX_SIZE=8 of MT_RX_BUF_SIZE=2k buffers for sg_en case. > > > > I thought the reason is that max AMSDU size is 16kB so it fit into > > > > 8 sg buffers of 2k. > > > > > > > > In other words, for me, looks like either > > > > - we can not handle AMSDU for non sg case because we do not > > > > allocate big enough buffer > > > > > > I think AMSDU is mandatory and we currently support it even for non-sg > > > case > > > (since max rx AMSDU is 3839B) > > > > > > > or > > > > - we can just use one PAGE_SIZE buffer for rx and remove sg > > > > buffers for rx completely > > > > > > using sg buffers we can support bigger rx AMSDU size in the future > > > without using > > > huge buffers (e.g. we can try to use IEEE80211_MAX_MPDU_LEN_HT_7935 with > > > mt76x2u) > > > > I think it would be simpler just to allocate 2 pages for 7935B . > > And if we could determine that there is no true need to use sg for rx, > I think best approach here would be revert f8f527b16db5 in v5.2 to fix > regression and remove rx sg in -next. That would make code simpler, > allocate 4k instead 16k per packet, allow to use build_skb (4096 - 3839 > give enough space for shared info) and not use usb hcd bounce buffer.
I do not think we should drop sg support since: - it allow us to rx huge amsdu frames (e.g. IEEE80211_MAX_MPDU_LEN_VHT_11454) using multiple one page buffer. I think there will be new usb devices where we can increase amsdu size (we can increase it even on mt76x2u usb 3.0 devices) - without SG we can't use build_skb() without copying a given size of the packet since the space needed for skb_shared_info is 320B on a x86_64 device - the fix for f8f527b16db5 has been already tested Regards, Lorenzo > > Stanislaw
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