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

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Message-ID: <56150DCB.70705@oracle.com>
Date:	Wed, 07 Oct 2015 20:19:23 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Roger Pau Monné <roger.pau@...rix.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


On 10/07/2015 07:46 PM, Roger Pau Monné wrote:
> 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);
> 

I'm worry about complains about more memory consumption if set to 4 by default.
Anyway, if you think it's fine I'll update the default value to 4 in next version.

-- 
Regards,
-Bob
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