netdev - Re: RPS vs RFS

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CA+mtBx9aF0XTG8wtBB2W7Be5o3PrbKZ_EWRuSoD73q=gvoT6AQ@mail.gmail.com>
Date:	Thu, 3 Apr 2014 16:58:43 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Sharat Masetty <sharat04@...il.com>
Cc:	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: RPS vs RFS

On Thu, Apr 3, 2014 at 12:14 PM, Sharat Masetty <sharat04@...il.com> wrote:
> I am trying to understand the true benefit of RFS over RPS. In the
> kernel documentation scaling.txt, the author talks about data cache
> hitrate, can someone explain what this actually means? In which
> scenarios would RFS be beneficial? Why would it help to have network
> stack run on the same core on which the application for a stream/flow
> is running?
>
Silo'ing processing is typically good, it provides cache locality,
potentially eliminates a cross CPU wakeup, and hopefully reduces lock
contention. There is a secondary benefit in that we get some isolation
of RX processing and application.
>
> Consider a NIC with a single receive queue, single interrupt line, and
> iperf application is pulling data off this NIC card. In case where
> iperf may still be running on the same core on which the interrupts
> are delivered, then in that case the whole stack is pinned to the same
> core, and would not be benefiting a lot from this scheme
>
Consider what happens you have a multi threaded network intensive
application like a web server. Running all the networking an a single
CPU becomes a bottleneck (why we created RPS/RFS in the first place).

>
>
>
> References:
> https://www.kernel.org/doc/Documentation/networking/scaling.txt
>
> https://lwn.net/Articles/382428/
>
> Regards,
> Sharat
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html