linux-toradex.git/drivers/s390/cio/css.c, branch v3.18.21

s390/css: Prevent unnecessary allocation in subchannel loop

2013-12-16T13:37:42+00:00

Subchannel looping function for_each_subchannel_staged() allocates a
subchannel-ID-bitmap to efficiently iterate over the list of known
and unknown subchannels. Since this function is also used to iterate
over known-subchannels only, optimize that case by not requiring the
ID-bitmap allocation and falling back to simple bus_for_each_dev()
looping.

Signed-off-by: Peter Oberparleiter 
Reviewed-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky

s390/cio: Delay scan for newly available I/O devices

2013-12-16T13:37:41+00:00

The CIO layer scans for newly available I/O devices by performing a scan
of available subchannels using the Store Subchannel (STSCH) instruction.
Performing too many STSCH instructions in a tight loop can cause high
Hypervisor overhead which can negatively impact the performance of the
virtual machine as a whole.

A subchannel scan is triggered for example during a hardware event that
indicates that a channel path has become available. It is also triggered
by the DASD device driver for each device that is set online.

This patch reduces the number of STSCH instructions being performed by
delaying the start of the actual subchannel scan by 1 second. Multiple
scan requests that are scheduled during this time will be merged into a
single scan loop.

The trade-off consists of a short delay that is introduced between
the time that the event is processed and a newly available device
becoming usable. This delay should be acceptable since it only
affects devices that have not been in use before.

Signed-off-by: Peter Oberparleiter 
Reviewed-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky

s390/cio: Relax subchannel scan loop

2013-12-16T13:37:40+00:00

The CIO layer scans for newly available I/O devices by performing a scan
of available subchannels using the Store Subchannel (STSCH) instruction.
This processing can take a significant amount of time during which no
other task can run on the same CPU (unless CONFIG_PREEMPT has been
enabled). As a result, scheduling latencies for other tasks are
increased noticeably, especially on a single-CPU system.

Fix this problem by explicitly allowing other tasks to be scheduled
each time a subchannel has been processed.

Signed-off-by: Peter Oberparleiter 
Reviewed-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky

s390/cio: fix unlocked access of global bitmap

2013-08-30T06:57:22+00:00

Access to the slow_subchannel_set has to be secured via the
slow_subchannel_lock.

Signed-off-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky

s390: replace strict_strtoul() with kstrtoul()

2013-08-22T10:20:00+00:00

The usage of strict_strtoul() is not preferred, because
strict_strtoul() is obsolete. Thus, kstrtoul() should be
used.

Signed-off-by: Jingoo Han 
Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky

s390/css: move subchannel lock allocation

2013-04-17T12:07:34+00:00

cio_validate_subchannel is used to do some basic checks to find out
if it's worth to further investigate a subchannel. Move the allocation
and initialization of the subchannels locks to css_alloc_subchannel.

Clean up the functions involved while at it.

Reviewed-by: Peter Oberparleiter 
Signed-off-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky

s390/css: remove unused function definitions

2013-04-17T12:07:33+00:00

Make css_probe_device static and remove an unimplemented prototype.

Reviewed-by: Peter Oberparleiter 
Signed-off-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky

s390/css: introduce cio_register_early_subchannels

2013-04-17T12:07:32+00:00

Use cio_register_early_subchannels to register early subchannels
which are already in use. Call this function before we do the
actual subchannel scanning loop. This helps us to get rid of some
more special cases regarding the console subchannel.

Reviewed-by: Peter Oberparleiter 
Signed-off-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky

s390/cio: get rid of static console subchannel

2013-04-17T12:07:32+00:00

Remove the static console subchannel (and friends) and use dynamic
allocation for these structures. With this change the console
subchanel is treated (mostly) like any other subchannel and we can
remove some special cases.

Reviewed-by: Peter Oberparleiter 
Signed-off-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky

s390/cio: split subchannel registration

2013-04-17T12:07:31+00:00

Split the subchannel registration in device_initialize and device_add
and move the initialization part inside the allocation function. With
this change we can use refcounting during the complete lifespan of a
subchannel which is important for devices where we do the actually
registration at a later time.

Reviewed-by: Peter Oberparleiter 
Signed-off-by: Sebastian Ott 
Signed-off-by: Martin Schwidefsky