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)
Another downside is that the SCSI device class lock is held during
the executions of ses_enclosure_data_process() since it's a callee
of ses_intf_add(), which is executed under that lock in device_add().
This ends up blocking the parallel SCSI scan functionality because
device_add() depends on that lock, and also the removal of devices
via device_del() (e.g., during an enclosure reboot).
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.
So, for out-of-tree modules and people still interested in this
behavior (in case I might have missed something about it, other
than the total probe time impact): let's add a module parameter
to keep that check turned on (disabled by default).
Also, 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@xxxxxxxxxxxxxxxxxx>
Fixes: 08024885a2a3 ("ses: Add power_status to SES device slot")
---
drivers/misc/enclosure.c | 6 +++++-
drivers/scsi/ses.c | 9 ++++++++-
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/drivers/misc/enclosure.c b/drivers/misc/enclosure.c
index 65fed7146e9b..d3a8a13c4247 100644
--- a/drivers/misc/enclosure.c
+++ b/drivers/misc/enclosure.c
@@ -148,7 +148,7 @@ struct enclosure_device *
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 +594,10 @@ static ssize_t get_component_power_status(struct device *cdev,
if (edev->cb->get_power_status)
edev->cb->get_power_status(edev, ecomp);
+
+ if (ecomp->power_status == -1)
+ return -EINVAL;
+
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..2fafefd419c1 100644
--- a/drivers/scsi/ses.c
+++ b/drivers/scsi/ses.c
@@ -36,6 +36,12 @@
#include <scsi/scsi_transport_sas.h>
+static bool power_status_on_probe; /* default: false, 0. */
+module_param(power_status_on_probe, bool, 0644);
+MODULE_PARM_DESC(power_status_on_probe, "get power status of SES device slots "
+ "(enclosure components) at probe time "
+ "(warning: may delay total probe time)");
+
struct ses_device {
unsigned char *page1;
unsigned char *page1_types;
@@ -548,7 +554,8 @@ 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 (power_status_on_probe)
+ ses_get_power_status(edev, ecomp);
if (addl_desc_ptr)
ses_process_descriptor(
ecomp,
--
1.8.3.1
