netdev - Re: [PATCH net-next] net/tcp: move TCP hash fail messages out of line

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Message-ID: <2d9e139d-2b7c-4edc-bb5f-32d067598e5c@intel.com>
Date: Thu, 4 Apr 2024 10:57:54 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Dmitry Safonov <dima@...sta.com>
CC: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Francesco Ruggeri <fruggeri@...sta.com>, "Salam
 Noureddine" <noureddine@...sta.com>, David Ahern <dsahern@...nel.org>,
	<nex.sw.ncis.osdt.itp.upstreaming@...el.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net/tcp: move TCP hash fail messages out of line

From: Dmitry Safonov <dima@...sta.com>
Date: Wed, 3 Apr 2024 18:00:49 +0100

> Hi Alexander,
> 
> On Wed, Apr 3, 2024 at 2:26 PM Alexander Lobakin
> <aleksander.lobakin@...el.com> wrote:
>>
>> tcp_hash_fail() is used multiple times on hotpath, including static
>> inlines. It contains a couple branches and a lot of code, which all
>> gets inlined into the call sites. For example, one call emits two
>> calls to net_ratelimit() etc.
>> Move as much as we can out of line to a new global function. Use enum
>> to determine the type of failure. Check for net_ratelimit() only once,
>> format common fields only once as well to pass only unique strings to
>> pr_info().
>> The result for vmlinux with Clang 19:
>>
>> add/remove: 2/0 grow/shrink: 0/4 up/down: 773/-4908 (-4135)
>> Function                                     old     new   delta
>> __tcp_hash_fail                                -     757    +757
>> __pfx___tcp_hash_fail                          -      16     +16
>> tcp_inbound_ao_hash                         1819    1062    -757
>> tcp_ao_verify_hash                          1217     451    -766
>> tcp_inbound_md5_hash                        1591     374   -1217
>> tcp_inbound_hash                            3566    1398   -2168
> 
> I can see that as an improvement, albeit that enum and the resulting switch
> are quite gross, sorry.

I know, but that's the only way to move that print out of line.

> I had patches to convert those messages to tracepoints (by Jakub's suggestion).
> That seems to work quite nice and will remove this macro entirely:
> https://lore.kernel.org/all/20240224-tcp-ao-tracepoints-v1-0-15f31b7f30a7@arista.com/

Oh sorry, I didn't search lore for the related patches before sending.
Sounds good! My solution can be dropped then. Just make sure you have
the same code size reduction in tcp_*_hash() :D

> 
> I need to send version 2 for that. Unfortunately, that got delayed by
> me migrating
> from my previous work laptop. That was not my choice, resulting in
> little disruption.
> I'm planning to send the new version optimistically by the end of this week,
> at worst the next week.
> 
> Thanks,
>             Dmitry

Thanks,
Olek