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authorMauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>2017-04-05 18:18:19 +0300
committerMartin K. Petersen <martin.petersen@oracle.com>2017-04-06 19:48:05 +0300
commit75106523f39751390b5789b36ee1d213b3af1945 (patch)
tree366f72c5827fb04e775090069439cc7fcb0a6317 /drivers/scsi/ses.c
parented12e031b0deb0268cc6ed2d6c49dbcbec1cf038 (diff)
downloadlinux-75106523f39751390b5789b36ee1d213b3af1945.tar.xz
scsi: ses: don't get power status of SES device slot on probe
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@linux.vnet.ibm.com> Fixes: 08024885a2a3 ("ses: Add power_status to SES device slot") Reviewed-by: Dan Williams <dan.j.williams@intel.com> Reviewed-by: Song Liu <songliubraving@fb.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Diffstat (limited to 'drivers/scsi/ses.c')
-rw-r--r--drivers/scsi/ses.c1
1 files changed, 0 insertions, 1 deletions
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,