Re: [RFC] [PATCH] Don't run __qdisc_run() on a stopped TX queue
From: Herbert Xu <herbert@gondor.apana.org.au>
Date: 2009-07-29 00:44:38
On Tue, Jul 28, 2009 at 12:59:19PM -0700, David Miller wrote:
The premise is that there'd be only one. The qdisc lock. If the traffic is distributed, flow wise, the driver XMIT lock would spread due to multiqueue.
Suppose that we have a single large flow going through that has filled up the hardware queue and is now backlogged in the qdisc with qdisc_run on CPU A. Now some other flow comes along and sends a packet on CPU B. So now CPU A and B will both be processing packets for the first flow causing loads of lock contention. But worse yet, we have introduced packet reordering. So are you convinced now :) Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} [off-list ref] Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt