Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <790ca4e6-e0c0-b454-6a50-f2e907523dd9@gmail.com>
Date:   Thu, 28 Apr 2022 16:11:45 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.8.1
Subject: Re: [PATCH net-next 02/11] udp/ipv6: refactor udpv6_sendmsg udplite
 checks
Content-Language: en-US
To:     Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>
Cc:     David Ahern <dsahern@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        linux-kernel@vger.kernel.org
References: <cover.1651071843.git.asml.silence@gmail.com>
 <33dfdf2119c86e35062f783d405bedec2fde2b4c.1651071843.git.asml.silence@gmail.com>
 <229c169ccf8fdbf7fc826901982f1f15e86f3d17.camel@redhat.com>
From:   Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <229c169ccf8fdbf7fc826901982f1f15e86f3d17.camel@redhat.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

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