netdev - Re: [RFC] [PATCH] Don't run __qdisc

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: <20090729112614.GB5490@ff.dom.local>
Date:	Wed, 29 Jul 2009 11:26:14 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, krkumar2@...ibm.com,
	netdev@...r.kernel.org
Subject: Re: [RFC] [PATCH] Don't run __qdisc_run() on a stopped TX queue

On Wed, Jul 29, 2009 at 07:11:34PM +0800, Herbert Xu wrote:
> On Wed, Jul 29, 2009 at 11:04:36AM +0000, Jarek Poplawski wrote:
> >
> > How about this: instead of the _RUNNING flag we take tx lock while
> > holding qdisc lock and release qdisc lock just after (before xmit).
> > This should prevent reordering, and probably could improve cache use:
> > CPU B which takes qdisc lock only for enqueuing now, would use it for
> > dequeuing too, plus if accidentally the next xmit goes to a different
> > tx queue, it could start before CPU A finishes. Otherwise it would
> > simply wait for CPU A (without tx lock contention). Of course it
> > needs testing... 
> 
> Well reordering isn't the only problem, the lock contention brought
> upon by two CPUs both trying to transmit the same flow from the
> qdisc is just as bad.

If you mean the tx lock there should be no "real" contention: only
one waiter max. qdisc lock's contention might be higher, but it's
use (during contention) better: enqueue + dequeue together instead
of doing it separately.

Cheers,
Jarek P.
--
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