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Filename Latest commit message Latest commit date
Eric Dumazet a05fb4ac72 virtio_net: Do not pull payload in skb->head
[ Upstream commit 0f6925b3e8da0dbbb52447ca8a8b42b371aac7db ]

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.

Fixes: 3226b158e67c ("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: Sasha Levin <sashal@kernel.org>
2021-05-22 11:38:28 +02:00
arch x86/msr: Fix wr/rdmsr_safe_regs_on_cpu() prototypes 2021-05-22 11:38:27 +02:00
block blk-mq: Swap two calls in blk_mq_exit_queue() 2021-05-19 10:08:30 +02:00
certs certs: Fix blacklist flag type confusion 2021-03-04 10:26:29 +01:00
crypto crypto: rng - fix crypto_rng_reset() refcounting when !CRYPTO_STATS 2021-05-11 14:04:15 +02:00
Documentation ARM: 9012/1: move device tree mapping out of linear region 2021-05-19 10:08:32 +02:00
drivers virtio_net: Do not pull payload in skb->head 2021-05-22 11:38:28 +02:00
fs f2fs: fix error handling in f2fs_end_enable_verity() 2021-05-19 10:08:32 +02:00
include virtio_net: Do not pull payload in skb->head 2021-05-22 11:38:28 +02:00
init init/Kconfig: make COMPILE_TEST depend on HAS_IOMEM 2021-04-10 13:34:32 +02:00
ipc
kernel kernel: kexec_file: fix error return code of kexec_calculate_store_digests() 2021-05-19 10:08:28 +02:00
lib kobject_uevent: remove warning in init_uevent_argv() 2021-05-19 10:08:33 +02:00
LICENSES
mm mm/hugetlb: fix F_SEAL_FUTURE_WRITE 2021-05-19 10:08:29 +02:00
net xsk: Simplify detection of empty and full rings 2021-05-22 11:38:27 +02:00
samples samples/bpf: Fix broken tracex1 due to kprobe argument change 2021-05-19 10:08:23 +02:00
scripts kconfig: nconf: stop endless search loops 2021-05-19 10:08:23 +02:00
security security: commoncap: fix -Wstringop-overread warning 2021-05-11 14:04:16 +02:00
sound ASoC: rsnd: check all BUSIF status when error 2021-05-19 10:08:33 +02:00
tools selftests: Set CC to clang in lib.mk if LLVM is set 2021-05-19 10:08:22 +02:00
usr
virt KVM: Stop looking for coalesced MMIO zones if the bus is destroyed 2021-05-14 09:44:15 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
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COPYING
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Kbuild
Kconfig
MAINTAINERS
Makefile Linux 5.4.120 2021-05-19 10:08:33 +02:00
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.

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.