ACK: [SRU Y/Z][PATCH] scsi: ses: don't get power status of SES device slot on probe

[Stefan Bader]

On 07.06.2017 20:49, Mauricio Faria de Oliveira wrote:
> BugLink: https://bugs.launchpad.net/bugs/1696445
> 
> The commit 08024885a2a3 ("ses: Add power_status to SES device slot")
> introduced the 'power_status' attribute to enclosure components and
> the associated callbacks.
> 
> There are 2 callbacks available to get the power status of a device:
> 1) ses_get_power_status() for 'struct enclosure_component_callbacks'
> 2) get_component_power_status() for the sysfs device attribute
> (these are available for kernel-space and user-space, respectively.)
> 
> However, despite both methods being available to get power status
> on demand, that commit also introduced a call to get power status
> in ses_enclosure_data_process().
> 
> This dramatically increased the total probe time for SCSI devices
> on larger configurations, because ses_enclosure_data_process() is
> called several times during the SCSI devices probe and loops over
> the component devices (but that is another problem, another patch).
> 
> That results in a tremendous continuous hammering of SCSI Receive
> Diagnostics commands to the enclosure-services device, which does
> delay the total probe time for the SCSI devices __significantly__:
> 
>   Originally, ~34 minutes on a system attached to ~170 disks:
> 
>     [ 9214.490703] mpt3sas version 13.100.00.00 loaded
>     ...
>     [11256.580231] scsi 17:0:177:0: qdepth(16), tagged(1), simple(0),
>                    ordered(0), scsi_level(6), cmd_que(1)
> 
>   With this patch, it decreased to ~2.5 minutes -- a 13.6x faster
> 
>     [ 1002.992533] mpt3sas version 13.100.00.00 loaded
>     ...
>     [ 1151.978831] scsi 11:0:177:0: qdepth(16), tagged(1), simple(0),
>                    ordered(0), scsi_level(6), cmd_que(1)
> 
> Back to the commit discussion.. on the ses_get_power_status() call
> introduced in ses_enclosure_data_process(): impact of removing it.
> 
> That may possibly be in place to initialize the power status value
> on device probe.  However, those 2 functions available to retrieve
> that value _do_ automatically refresh/update it.  So the potential
> benefit would be a direct access of the 'power_status' field which
> does not use the callbacks...
> 
> But the only reader of 'struct enclosure_component::power_status'
> is the get_component_power_status() callback for sysfs attribute,
> and it _does_ check for and call the .get_power_status callback,
> (which indeed is defined and implemented by that commit), so the
> power status value is, again, automatically updated.
> 
> So, the remaining potential for a direct/non-callback access to
> the power_status attribute would be out-of-tree modules -- well,
> for those, if they are for whatever reason interested in values
> that are set during device probe and not up-to-date by the time
> they need it.. well, that would be curious.
> 
> Well, to handle that more properly, set the initial power state
> value to '-1' (i.e., uninitialized) instead of '1' (power 'on'),
> and check for it in that callback which may do an direct access
> to the field value _if_ a callback function is not defined.
> 
> Signed-off-by: Mauricio Faria de Oliveira <mauricfo at linux.vnet.ibm.com>
> Fixes: 08024885a2a3 ("ses: Add power_status to SES device slot")
> Reviewed-by: Dan Williams <dan.j.williams at intel.com>
> Reviewed-by: Song Liu <songliubraving at fb.com>
> Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
> (cherry picked from commit 75106523f39751390b5789b36ee1d213b3af1945)
> Signed-off-by: Mauricio Faria de Oliveira <mauricfo at linux.vnet.ibm.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>

> ---
>  drivers/misc/enclosure.c | 7 ++++++-
>  drivers/scsi/ses.c       | 1 -
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/enclosure.c b/drivers/misc/enclosure.c
> index 65fed7146e9b..d3fe3ea902d4 100644
> --- a/drivers/misc/enclosure.c
> +++ b/drivers/misc/enclosure.c
> @@ -148,7 +148,7 @@ enclosure_register(struct device *dev, const char *name, int components,
>  	for (i = 0; i < components; i++) {
>  		edev->component[i].number = -1;
>  		edev->component[i].slot = -1;
> -		edev->component[i].power_status = 1;
> +		edev->component[i].power_status = -1;
>  	}
>  
>  	mutex_lock(&container_list_lock);
> @@ -594,6 +594,11 @@ static ssize_t get_component_power_status(struct device *cdev,
>  
>  	if (edev->cb->get_power_status)
>  		edev->cb->get_power_status(edev, ecomp);
> +
> +	/* If still uninitialized, the callback failed or does not exist. */
> +	if (ecomp->power_status == -1)
> +		return (edev->cb->get_power_status) ? -EIO : -ENOTTY;
> +
>  	return snprintf(buf, 40, "%s\n", ecomp->power_status ? "on" : "off");
>  }
>  
> diff --git a/drivers/scsi/ses.c b/drivers/scsi/ses.c
> index 50adabbb5808..f1cdf32d7514 100644
> --- a/drivers/scsi/ses.c
> +++ b/drivers/scsi/ses.c
> @@ -548,7 +548,6 @@ static void ses_enclosure_data_process(struct enclosure_device *edev,
>  					ecomp = &edev->component[components++];
>  
>  				if (!IS_ERR(ecomp)) {
> -					ses_get_power_status(edev, ecomp);
>  					if (addl_desc_ptr)
>  						ses_process_descriptor(
>  							ecomp,
> 


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