From: "Rafał Miłecki" <zajec5@gmail.com>
To: Network Development <netdev@vger.kernel.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Russell King <linux@armlinux.org.uk>,
Andrew Lunn <andrew@lunn.ch>, Felix Fietkau <nbd@nbd.name>
Cc: "openwrt-devel@lists.openwrt.org"
<openwrt-devel@lists.openwrt.org>,
Florian Fainelli <f.fainelli@gmail.com>
Subject: Optimizing kernel compilation / alignments for network performance
Date: Wed, 27 Apr 2022 14:04:54 +0200 [thread overview]
Message-ID: <84f25f73-1fab-fe43-70eb-45d25b614b4c@gmail.com> (raw)
Hi,
I noticed years ago that kernel changes touching code - that I don't use
at all - can affect network performance for me.
I work with home routers based on Broadcom Northstar platform. Those
are SoCs with not-so-powerful 2 x ARM Cortex-A9 CPU cores. Main task of
those devices is NAT masquerade and that is what I test with iperf
running on two x86 machines.
***
Example of such unused code change:
ce5013ff3bec ("mtd: spi-nor: Add support for XM25QH64A and XM25QH128A").
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ce5013ff3bec05cf2a8a05c75fcd520d9914d92b
It lowered my NAT speed from 381 Mb/s to 367 Mb/s (-3,5%).
I first reported that issue it in the e-mail thread:
ARM router NAT performance affected by random/unrelated commits
https://lkml.org/lkml/2019/5/21/349
https://www.spinics.net/lists/linux-block/msg40624.html
Back then it was commit 5b0890a97204 ("flow_dissector: Parse batman-adv
unicast headers")
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9316a9ed6895c4ad2f0cde171d486f80c55d8283
that increased my NAT speed from 741 Mb/s to 773 Mb/s (+4,3%).
***
It appears Northstar CPUs have little cache size and so any change in
location of kernel symbols can affect NAT performance. That explains why
changing unrelated code affects anything & it has been partially proven
aligning some of cache-v7.S code.
My question is: is there a way to find out & force an optimal symbols
locations?
Adding .align 5 to the cache-v7.S is a partial success. I'd like to find
out what other functions are worth optimizing (aligning) and force that
(I guess __attribute__((aligned(32))) could be used).
I can't really draw any conclusions from comparing System.map before and
after above commits as they relocate thousands of symbols in one go.
Optimizing is pretty important for me for two reasons:
1. I want to reach maximum possible NAT masquerade performance
2. I need stable performance across random commits to detect regressions
next reply other threads:[~2022-04-27 12:05 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-27 12:04 Rafał Miłecki [this message]
2022-04-27 12:56 ` Optimizing kernel compilation / alignments for network performance Alexander Lobakin
2022-04-27 17:31 ` Rafał Miłecki
2022-04-29 14:18 ` Rafał Miłecki
2022-04-29 14:49 ` Arnd Bergmann
2022-05-05 15:42 ` Rafał Miłecki
2022-05-05 16:04 ` Andrew Lunn
2022-05-05 16:46 ` Felix Fietkau
2022-05-06 7:47 ` Rafał Miłecki
2022-05-06 12:42 ` Andrew Lunn
2022-05-10 10:29 ` Rafał Miłecki
2022-05-10 14:09 ` Dave Taht
2022-05-10 19:15 ` Dave Taht
2022-05-06 7:44 ` Rafał Miłecki
2022-05-06 8:45 ` Arnd Bergmann
2022-05-06 8:55 ` Rafał Miłecki
2022-05-06 9:44 ` Arnd Bergmann
2022-05-10 12:51 ` Rafał Miłecki
2022-05-10 13:19 ` Arnd Bergmann
2022-05-10 11:23 ` Rafał Miłecki
2022-05-10 13:18 ` Arnd Bergmann
2022-05-08 9:53 ` Rafał Miłecki
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