netdev - Re: Netperf UDP issue with connected sockets

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

Message-ID: <1479388850.8455.240.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 17 Nov 2016 05:20:50 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Rick Jones <rick.jones2@....com>, netdev@...r.kernel.org
Subject: Re: Netperf UDP issue with connected sockets

On Thu, 2016-11-17 at 09:16 +0100, Jesper Dangaard Brouer wrote:

> 
> I noticed there is a Send-Q, and the perf-top2 is _raw_spin_lock, which
> looks like it comes from __dev_queue_xmit(), but we know from
> experience that this stall is actually caused by writing the
> tailptr/doorbell in the HW.  Thus, this could benefit a lot from
> bulk/xmit_more into the qdisc layer.

The Send-Q is there because of TX-completions being delayed a bit,
because of IRQ mitigation.

(ethtool -c eth0)

It happens even if you do not have a qdisc in the first place.

And we do have xmit_more in the qdisc layer already.