netdev - Re: [PATCH] ifb: add multi-queue support

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]

Date:	Mon, 16 Nov 2009 09:19:21 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	xiaosuo@...il.com
CC:	"David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...tta.com>,
	Patrick McHardy <kaber@...sh.net>,
	Tom Herbert <therbert@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] ifb: add multi-queue support

Changli Gao a écrit :
> ifb: add multi-queue support.
> 
> Add multi-queue support, through more than one tasklets. One tasklet per
> queue always steers on the same CPU, and if the number of the
> tasklets(queues) is lager than the number of CPUs, more than one
> tasklets will be assigned to the same CPU.
> 
> Signed-off-by: Changli Gao <xiaosuo@...il.com>
> ----

> 

I must say I fail to see how multiple tasklets per cpu can be of any use.

And :

+	if (skb_queue_len(&pq->rq) == 1)
+		tasklet_schedule_on(&pq->task, num % num_online_cpus());

Is probably not what you want, because :

A) num_online_cpus() can be expensive to compute,
B) and you can have such configs :

Three online cpus, CPU0 and CPU4, CPU5
-> you call tasklet_schedule_on(... , num = {0|1|2})

To avoid packets reorder, if your hash function selects an offline cpu,
you must forward the packet to a particular cpu, regardless of cpu currently running.
(even if real device is not multiqueue, its RX interrupts can be handled by any online cpu)

You maybe need to maintain a mapping table with cpu hotplug notifiers.
--
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