linux-kernel - Re: [PATCH v2 17/17] ibmvfc: provide modules parameters for MQ settings

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Message-ID: <7d9a1415-4c0b-15df-1b79-ef2e760f57c1@linux.ibm.com>
Date:   Wed, 2 Dec 2020 14:17:37 -0800
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     Brian King <brking@...ux.vnet.ibm.com>,
        james.bottomley@...senpartnership.com
Cc:     martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        brking@...ux.ibm.com
Subject: Re: [PATCH v2 17/17] ibmvfc: provide modules parameters for MQ
 settings

On 12/2/20 10:40 AM, Brian King wrote:
> On 12/1/20 6:53 PM, Tyrel Datwyler wrote:
>> +module_param_named(mig_channels_only, mig_channels_only, uint, S_IRUGO | S_IWUSR);
>> +MODULE_PARM_DESC(mig_channels_only, "Prevent migration to non-channelized system. "
>> +		 "[Default=" __stringify(IBMVFC_MIG_NO_SUB_TO_CRQ) "]");
>> +module_param_named(mig_no_less_channels, mig_no_less_channels, uint, S_IRUGO | S_IWUSR);
>> +MODULE_PARM_DESC(mig_no_less_channels, "Prevent migration to system with less channels. "
>> +		 "[Default=" __stringify(IBMVFC_MIG_NO_N_TO_M) "]");
> 
> Both of these are writeable, but it doesn't look like you do any re-negotiation
> with the VIOS for these changed settings to take effect if someone changes
> them at runtime.

For some reason I convinced myself that these could just be changed on the fly,
but yes for them to actually take effect we need to re-negotiate the channels setup.

> 
>> +
>>  module_param_named(init_timeout, init_timeout, uint, S_IRUGO | S_IWUSR);
>>  MODULE_PARM_DESC(init_timeout, "Initialization timeout in seconds. "
>>  		 "[Default=" __stringify(IBMVFC_INIT_TIMEOUT) "]");
> 
>> @@ -3228,6 +3250,36 @@ static ssize_t ibmvfc_store_log_level(struct device *dev,
>>  	return strlen(buf);
>>  }
>>  
>> +static ssize_t ibmvfc_show_scsi_channels(struct device *dev,
>> +					 struct device_attribute *attr, char *buf)
>> +{
>> +	struct Scsi_Host *shost = class_to_shost(dev);
>> +	struct ibmvfc_host *vhost = shost_priv(shost);
>> +	unsigned long flags = 0;
>> +	int len;
>> +
>> +	spin_lock_irqsave(shost->host_lock, flags);
>> +	len = snprintf(buf, PAGE_SIZE, "%d\n", vhost->client_scsi_channels);
>> +	spin_unlock_irqrestore(shost->host_lock, flags);
>> +	return len;
>> +}
>> +
>> +static ssize_t ibmvfc_store_scsi_channels(struct device *dev,
>> +					 struct device_attribute *attr,
>> +					 const char *buf, size_t count)
>> +{
>> +	struct Scsi_Host *shost = class_to_shost(dev);
>> +	struct ibmvfc_host *vhost = shost_priv(shost);
>> +	unsigned long flags = 0;
>> +	unsigned int channels;
>> +
>> +	spin_lock_irqsave(shost->host_lock, flags);
>> +	channels = simple_strtoul(buf, NULL, 10);
>> +	vhost->client_scsi_channels = min(channels, nr_scsi_hw_queues);
> 
> Don't we need to do a LIP here for this new setting to go into effect?

Actually, we need a hard reset to break the CRQ Pair. A LIP will only do a NPIV
Logout/Login which keeps the existing channel setup.

-Tyrel

> 
>> +	spin_unlock_irqrestore(shost->host_lock, flags);
>> +	return strlen(buf);
>> +}
>> +
>>  static DEVICE_ATTR(partition_name, S_IRUGO, ibmvfc_show_host_partition_name, NULL);
>>  static DEVICE_ATTR(device_name, S_IRUGO, ibmvfc_show_host_device_name, NULL);
>>  static DEVICE_ATTR(port_loc_code, S_IRUGO, ibmvfc_show_host_loc_code, NULL);
> 
> 
>