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From: "Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@intel.com>
To: "Jarek Poplawski" <jarkao2@o2.pl>, "Thomas Graf" <tgraf@suug.ch>
Cc: "Kok, Auke-jan H" <auke-jan.h.kok@intel.com>,
	"David Miller" <davem@davemloft.net>,
	"Garzik, Jeff" <jgarzik@pobox.com>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@intel.com>,
	"Kok, Auke" <auke@foo-projects.org>,
	"Ronciak, John" <john.ronciak@intel.com>
Subject: RE: [PATCH 1/2] NET: Multiple queue network device support
Date: Mon, 12 Mar 2007 13:21:16 -0700	[thread overview]
Message-ID: <D5C1322C3E673F459512FB59E0DDC329027335CC@orsmsx414.amr.corp.intel.com> (raw)
In-Reply-To: <20070312085802.GA1664@ff.dom.local>


> -----Original Message-----
> From: Jarek Poplawski [mailto:jarkao2@o2.pl] 
> Sent: Monday, March 12, 2007 1:58 AM
> To: Thomas Graf
> Cc: Kok, Auke-jan H; David Miller; Garzik, Jeff; 
> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; 
> Waskiewicz Jr, Peter P; Brandeburg, Jesse; Kok, Auke; Ronciak, John
> Subject: Re: [PATCH 1/2] NET: Multiple queue network device support
> 
> On 09-03-2007 14:40, Thomas Graf wrote:
> > * Kok, Auke <auke-jan.h.kok@intel.com> 2007-02-08 16:09
> >> diff --git a/net/core/dev.c b/net/core/dev.c index 
> 455d589..42b635c 
> >> 100644
> >> --- a/net/core/dev.c
> >> +++ b/net/core/dev.c
> >> @@ -1477,6 +1477,49 @@ gso:
> >>  	skb->tc_verd = SET_TC_AT(skb->tc_verd,AT_EGRESS);
> >>  #endif
> >>  	if (q->enqueue) {
> >> +#ifdef CONFIG_NET_MULTI_QUEUE_DEVICE
> >> +		int queue_index;
> >> +		/* If we're a multi-queue device, get a queue 
> index to lock */
> >> +		if (netif_is_multiqueue(dev))
> >> +		{
> >> +			/* Get the queue index and lock it. */
> >> +			if (likely(q->ops->map_queue)) {
> >> +				queue_index = q->ops->map_queue(skb, q);
> >> +				
> spin_lock(&dev->egress_subqueue[queue_index].queue_lock);
> >> +				rc = q->enqueue(skb, q);
> 
> I'm not sure Dave Miller thought about this place, when he 
> proposed to save the mapping, but I think this could be not 
> enough. This place is racy: ->map_queue() is called 2 times 
> and with some filters (and
> policies/actions) results could differ. And of course the 
> subqueue lock doesn't prevent any filter from a config change 
> in the meantime.
> 
> After second reading of this patch I have doubts it's the 
> proper way to solve the problem: there are many subqueues but 
> we need a top queue (prio here) to mange them, anyway. So, 
> why not to build this functionality directly into the queue? 
> There is no difference for a device if skbs are going from 
> the subqueue or a class, it is only interested in the mapping 
> result and a possibility to stop and start a subqueue and to 
> query its status. All this could be done by adding the 
> callbacks directly to any classful scheduler or, if not 
> enough, to write some specialized qdisc based on prio. The 
> possibility to lock only a subqueue instead of a queue could 
> be analized independently - current proposal doesn't solve 
> this anyway.
> 
> Regards,
> Jarek P.
> 

Thanks again for the feedback.  Given some discussions I had last week
in the office and the general feedback here, I'm going to remove the new
per-queue locking and leave the start/stop functions for each queue and
combine entry points for hard_start_xmit().  I'll get this out asap for
review once it's been tested here.  If we see issues in the future with
lock contention on the queues, we can revisit the per-queue locking.

Cheers,
-PJ Waskiewicz

  reply	other threads:[~2007-03-12 20:21 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-09  0:09 [PATCH 0/2 REVIEW] Multiple transmit/receive queue kernel Kok, Auke
2007-02-09  0:09 ` [PATCH 1/2] NET: Multiple queue network device support Kok, Auke
2007-02-27  1:03   ` David Miller
2007-02-27 19:38     ` Waskiewicz Jr, Peter P
2007-03-07 22:18     ` Waskiewicz Jr, Peter P
2007-03-07 22:42       ` David Miller
2007-03-09  7:26         ` Jarek Poplawski
2007-03-09 13:40   ` Thomas Graf
2007-03-09 19:25     ` Waskiewicz Jr, Peter P
2007-03-09 23:01       ` Thomas Graf
2007-03-09 23:27         ` Waskiewicz Jr, Peter P
2007-03-10  2:34           ` Thomas Graf
2007-03-10 20:37             ` Waskiewicz Jr, Peter P
2007-03-12  8:58     ` Jarek Poplawski
2007-03-12 20:21       ` Waskiewicz Jr, Peter P [this message]
2007-02-09  0:09 ` [PATCH 2/2] e1000: Implement the new kernel API for multiqueue TX support Kok, Auke
2007-03-09 13:11   ` Thomas Graf
2007-02-23  9:00 [PATCH 1/2] NET: Multiple queue network device support Sreenivasa Honnur
2007-02-23 19:05 ` Waskiewicz Jr, Peter P
2007-02-23 19:19 ` Stephen Hemminger
2007-02-23 19:23   ` Kok, Auke
2007-02-23  9:02 Sreenivasa Honnur

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