netdev - Re: Same data to several sockets with just one syscall ?

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Message-ID: <CAGWmfYru4zP1n7aSbjtpO4J=aCBfp47B8AV-ACv8XuY-n9E+Hg@mail.gmail.com>
Date:	Mon, 15 Feb 2016 11:03:01 +0100
From:	Claudio Scordino <claudio@...dence.eu.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Same data to several sockets with just one syscall ?

Hi Eric,

2016-02-12 11:35 GMT+01:00 Eric Dumazet <eric.dumazet@...il.com>:
> On Fri, 2016-02-12 at 09:53 +0100, Claudio Scordino wrote:
>
>> This makes the application waste time in entering/exiting the kernel
>> level several times.
>
> syscall overhead is usually small. Real cost is actually getting to the
> socket objects (fd manipulation), that you wont avoid with a
> super-syscall anyway.

Thank you for answering. I see your point.

However, assuming that a switch from user-space to kernel-space (and
back) needs about 200nsec of computation (which I guess is a
reasonable value for a 3GHz x86 architecture), the 50th receiver
experiences a latency of about 10 usec. In some domains (e.g.,
finance) this delay is not negligible.

Moving the "fan-out" code into kernel space would remove this waste of
time. IMHO, the latency reduction would pay back the 100 lines of code
for adding a new syscall.

Many thanks and best regards,

                 Claudio