virtio_net: Do not pull payload in skb->head Xuan Zhuo reported that commit 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") brought a ~10% performance drop. The reason for the performance drop was that GRO was forced to chain sk_buff (using skb_shinfo(skb)->frag_list), which uses more memory but also cause packet consumers to go over a lot of overhead handling all the tiny skbs. It turns out that virtio_net page_to_skb() has a wrong strategy : It allocates skbs with GOOD_COPY_LEN (128) bytes in skb->head, then copies 128 bytes from the page, before feeding the packet to GRO stack. This was suboptimal before commit 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") because GRO was using 2 frags per MSS, meaning we were not packing MSS with 100% efficiency. Fix is to pull only the ethernet header in page_to_skb() Then, we change virtio_net_hdr_to_skb() to pull the missing headers, instead of assuming they were already pulled by callers. This fixes the performance regression, but could also allow virtio_net to accept packets with more than 128bytes of headers. Many thanks to Xuan Zhuo for his report, and his tests/help. BUG=b/183655476 TEST=presubmit SOURCE=UPSTREAM(0f6925b3e8da0dbbb52447ca8a8b42b371aac7db) RELEASE_NOTE=avoid 32 x truesize under-estimation for tiny skbs This reverts commit 6ffbd6030f62a0cf9cc3d2750e0a81843a4df913. Reason for revert: Reland the changes cos-patch: bug Change-Id: I30235007954daa9e37f3abd96b47c64704c8dc39 Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/17372 Reviewed-by: Oleksandr Tymoshenko <ovt@google.com> Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com> Main-Branch-Verified: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com> 2 files changed
