Hi Jussi, Jussi Kivilinna <jussi.kivili...@haltian.com> writes: >> Jussi Kivilinna <jussi.kivili...@haltian.com> writes: >>> Enabling SG allows enabling GSO (generic segmentation offload) feature >>> of linux networking layer. This increases TCP throughput with NCM >>> on Cortex-A15+USB3380 based device from 300 Mbit/s to 1.1 Gbit/s. >>> >>> Signed-off-by: Jussi Kivilinna <jussi.kivili...@haltian.com> >> >> this is AWESOME!! :-) But here's the thing, any chance we can build this >> in u_ether.c ? Also, NETIF_F_SG should be conditional on >> gadget->sg_supported so that we don't break UDCs that don't support >> sglists. >> > > Actually, no sglists are passed to UDC. Reason why this work > with minimal changes for NCM is that NCM does tx buffering > in its wrap function.. 'ncm_wrap_ntb' copies input skbuffs to > larger skbuff, so enabling SG is only matter of changing that > skbuff data copy from 'memcpy' to 'skb_copy_bits' (and changing > CRC calculation work with skbuff fragments). Since NCM already > does copying, SG can be enabled for NCM without extra overhead.
aha, understood. Now what if we skip copying altogether? If we have an sg and a UDC that supports sg (gadget->sg_supported = 1), then we can avoid copying, right? > To see if NETIF_F_SG with skbuff copying made difference with > other networking gadgets, I made quick test for RNDIS gadget to > enable NETIF_F_SG by adding skb_linearize_cow call to > 'rndis_add_header' wrap function. TCP transfer from device to > host: > without SG: 265 Mbit/s > with SG: 326 Mbit/s > > So, adding NETIF_F_SG with skbuff linearization in u_ether > could improve performance little bit. interesting. Does USB3380 support sglists? We could check how much more we get if we skip copying altogether. > For higher speeds with USB3380/SuperSpeed, either larger MTU or > NCM (with its tx buffering) is needed. Here's earlier CDC EEM > results on different MTUs, without NETIF_F_SG change, on same hw: > MTU=1500: 169 Mbit/s > MTU=15000: 1.23 Gbit/s > > and on Intel PC + USB3380: > MTU=1500: 259 Mbit/s > MTU=3000: 452 Mbit/s > MTU=4500: 575 Mbit/s > MTU=9000: 823 Mbit/s > MTU=12000: 934 Mbit/s > MTU=15000: 1000 Mbit/s cool, thanks for these numbers. This is very interesting, indeed. -- balbi
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