netdev - Re: [PATCH net-next 02/11] udp/ipv6: refactor udpv6

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Message-ID: <790ca4e6-e0c0-b454-6a50-f2e907523dd9@gmail.com>
Date:   Thu, 28 Apr 2022 16:11:45 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 02/11] udp/ipv6: refactor udpv6_sendmsg udplite
 checks

On 4/28/22 15:09, Paolo Abeni wrote:
> On Thu, 2022-04-28 at 11:56 +0100, Pavel Begunkov wrote:
>> Don't save a IS_UDPLITE() result in advance but do when it's really
>> needed, so it doesn't store/load it from the stack. Same for resolving
>> the getfrag callback pointer.
> 
> It's quite unclear to me if this change brings really any performance
> benefit. The end results will depend a lot on the optimization
> performed by the compiler, and IMHO the code looks better before this
> modifications.

There is a lot of code and function calls between IS_UDPLITE() and
use sites, because of alias analysis the compiler will be forced
to call it early in the function and store something on stack.
I don't believe it will be able to keep in a register. But it's
not a problem to drop it

-- 
Pavel Begunkov