linux-kernel - Re: [PATCH v3 6/9] xen/blkfront: negotiate the number of hw queues/rings with backend

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Date:	Wed, 7 Oct 2015 13:46:13 +0200
From:	Roger Pau Monné <roger.pau@...rix.com>
To:	Bob Liu <bob.liu@...cle.com>
CC:	<xen-devel@...ts.xen.org>, <david.vrabel@...rix.com>,
	<linux-kernel@...r.kernel.org>, <konrad.wilk@...cle.com>,
	<felipe.franciosi@...rix.com>, <axboe@...com>, <hch@...radead.org>,
	<avanzini.arianna@...il.com>, <rafal.mielniczuk@...rix.com>,
	<boris.ostrovsky@...cle.com>, <jonathan.davies@...rix.com>
Subject: Re: [PATCH v3 6/9] xen/blkfront: negotiate the number of hw
 queues/rings with backend

El 07/10/15 a les 12.39, Bob Liu ha escrit:
> On 10/05/2015 10:40 PM, Roger Pau Monné wrote:
>> El 05/09/15 a les 14.39, Bob Liu ha escrit:
>>> @@ -2267,6 +2335,12 @@ static int __init xlblk_init(void)
>>>  		xen_blkif_max_ring_order = 0;
>>>  	}
>>>  
>>> +	if (xen_blkif_max_queues > nr_cpus) {
>>
>> Shouldn't there be a default value for xen_blkif_max_queues if the user
>> hasn't set the parameter on the command line?
>>
> 
> Then the default value is 0, multi-queue isn't enabled by default.

Why isn't it enabled by default with a sensible number of queues? I
guess something like:

if (xen_blkif_max_queues == 0)
	xen_blkif_max_queues = min(nr_cpus, 4);

Roger.
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