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Eric Dumazet 16851e34b6 virtio_net: Do not pull payload in skb->head 
commit 0f6925b3e8 upstream.

Xuan Zhuo reported that commit 3226b158e6 ("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 3226b158e6 ("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.

Fixes: 3226b158e6 ("net: avoid 32 x truesize under-estimation for tiny skbs")
Reported-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Link: https://www.spinics.net/lists/netdev/msg731397.html
Co-Developed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-08-04 12:23:44 +02:00
arch ARM: dts: versatile: Fix up interrupt controller node names 2021-07-31 08:22:38 +02:00
block blk-wbt: make sure throttle is enabled properly 2021-07-20 16:15:48 +02:00
certs certs: Fix blacklist flag type confusion 2021-03-04 09:39:44 +01:00
crypto crypto: shash - avoid comparing pointers to exported functions under CFI 2021-07-20 16:15:44 +02:00
Documentation clocksource: Retry clock read if long delays detected 2021-07-20 16:15:46 +02:00
drivers virtio_net: Do not pull payload in skb->head 2021-08-04 12:23:44 +02:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:21:29 +01:00
fs cifs: fix the out of range assignment to bit fields in parse_server_interfaces 2021-07-31 08:22:38 +02:00
include virtio_net: Do not pull payload in skb->head 2021-08-04 12:23:44 +02:00
init pid: take a reference when initializing cad_pid 2021-06-10 13:24:06 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:18:40 +02:00
kernel workqueue: fix UAF in pwq_unbound_release_workfn() 2021-07-31 08:22:37 +02:00
lib lib/decompress_unlz4.c: correctly handle zero-padding around initrds. 2021-07-20 16:16:10 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm: slab: fix kmem_cache_create failed when sysfs node not destroyed 2021-07-28 11:13:44 +02:00
net sctp: move 198 addresses from unusable to private scope 2021-07-31 08:22:38 +02:00
samples samples/bpf: Fix the error return code of xdp_redirect's main() 2021-07-20 16:15:51 +02:00
scripts kbuild: mkcompile_h: consider timestamp if KBUILD_BUILD_TIMESTAMP is set 2021-07-28 11:13:43 +02:00
security smackfs: restrict bytes count in smk_set_cipso() 2021-07-20 16:16:06 +02:00
sound ALSA: sb: Fix potential ABBA deadlock in CSP driver 2021-07-28 11:13:49 +02:00
tools selftest: fix build error in tools/testing/selftests/vm/userfaultfd.c 2021-07-31 08:22:37 +02:00
usr initramfs: restore default compression behavior 2020-04-13 10:44:59 +02:00
virt KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped() 2021-07-28 11:13:51 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Documentation/llvm: add documentation on building w/ Clang/LLVM 2020-09-26 18:01:31 +02:00
Makefile Linux 4.19.200 2021-07-31 08:22:38 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.