netdev - napi layer and packet throttling

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

Date:	Thu, 23 May 2013 13:52:46 +0200
From:	Holger Brunck <holger.brunck@...mile.com>
To:	netdev@...r.kernel.org
Subject: napi layer and packet throttling

Hi all,
I have a general question to the napi layer. I have a board with a MPC8360
processor which uses the ucc_geth.c driver for it's ethernet device. The kernel
version is 3.9. We see in lab tests that the board gets unresponsive if we send
a high packet rate to this ethernet device via an packet generator. In the end
we would like to limit the amount of incoming packets at a very early stage, to
prevent the system of a to high softirq load.

The NAPI layer description I read on:
http://www.linuxfoundation.org/collaborate/workgroups/networking/napi
pointed two main functions out for the napi layer.

a) Interrupt mitigation
Which works perfectly on the ucc_geth.c driver under high load the hard irqs for
the RX packets are disabled and we switch to a polling mode. If the load is more
relaxed we switch back.

b) Packet-Throttling
Here the description says "NAPI-compliant drivers can often cause packets to be
dropped in the network adaptor itself, before the kernel sees them at all."

This is exactly what I need for my usecase. But I don't see any hints how this
can be implemented with the napi layer. So what I need would be something like a
possibility to accept on the eth0 device in timeframe x only packetcount y. If
this packetcount is reached disable hard irq and napi_poll until the timeframe
is expired.

So are there any pointers to other ethernet drivers doing something like this?
Do I misunderstand the packet throttling purpose of the NAPI layer completely?

Any help is appreciated.

Regards
Holger

--
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