netdev - Re: [PATCH net-next] net: rps: don't skip offline cpus when set rps

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-Id: <20170515.102330.1406781282658945993.davem@davemloft.net>
Date:   Mon, 15 May 2017 10:23:30 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     zlpnobody@....com
Cc:     netdev@...r.kernel.org, therbert@...gle.com, zlpnobody@...il.com
Subject: Re: [PATCH net-next] net: rps: don't skip offline cpus when set
 rps_cpus

From: Liping Zhang <zlpnobody@....com>
Date: Mon, 15 May 2017 20:55:52 +0800

> From: Liping Zhang <zlpnobody@...il.com>
> 
> On our 4-core system, sometimes I can enable all CPUs to process packets.
> But sometimes I can't, if all the CPUs become offline except core 0, I
> will get the following result, which is really annoying for my script:
>  # echo f > /sys/class/net/eth0/queues/rx-0/rps_cpus
>  # cat /sys/class/net/eth0/queues/rx-0/rps_cpus
>  1
> 
> Since we won't steer the packets to these offline cpus, it's reasonable
> to enable all configed cpus to the rps_map, even if they are offline for
> the time being.
> 
> Signed-off-by: Liping Zhang <zlpnobody@...il.com>

But this means while those cpus are offline, get_rps_cpu() performs
very suboptimally.

In fact, if the packet hashes to one of those offline cpus, you get
no RPS at all.

So I think we really can't make this change, at least in it's current
form.