blk_lld_busy(9) [suse man page]

BLK_LLD_BUSY(9) 						   Block Devices						   BLK_LLD_BUSY(9)

NAME

       blk_lld_busy - Check if underlying low-level drivers of a device are busy

SYNOPSIS

       int blk_lld_busy(struct request_queue * q);

ARGUMENTS

       q
	   the queue of the device being checked

DESCRIPTION

       Check if underlying low-level drivers of a device are busy. If the drivers want to export their busy state, they must set own exporting
       function using blk_queue_lld_busy first.

       Basically, this function is used only by request stacking drivers to stop dispatching requests to underlying devices when underlying
       devices are busy. This behavior helps more I/O merging on the queue of the request stacking driver and prevents I/O throughput regression
       on burst I/O load.

RETURN

       0 - Not busy (The request stacking driver should dispatch request) 1 - Busy (The request stacking driver should stop dispatching request)

COPYRIGHT

Kernel Hackers Manual 2.6.					     July 2010							   BLK_LLD_BUSY(9)

drv_usecwait(9F)					   Kernel Functions for Drivers 					  drv_usecwait(9F)

NAME

       drv_usecwait - busy-wait for specified interval

SYNOPSIS

       #include <sys/types.h>
       #include <sys/ddi.h>

       void drv_usecwait(clock_t microsecs);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       microsecs       The number of microseconds to busy-wait.

DESCRIPTION

       drv_usecwait()  gives  drivers  a  means  of  busy-waiting  for a specified microsecond count. The amount of time spent busy-waiting may be
       greater than the microsecond count but will minimally be the number of microseconds specified.

       delay(9F) can be used by a driver to delay for a specified number of system ticks, but it has two limitations. First,  the  granularity	of
       the  wait  time	is limited to  one clock tick, which may be more time than is needed for the delay. Second,  delay(9F) may only be invoked
       from user context and hence cannot be used at interrupt time or system initialization.

       Often, drivers need to delay for only a few microseconds, waiting for a write to a device register to be picked up by the device.  In  this
       case, even in user context,  delay(9F) produces too long a wait period.

CONTEXT

       drv_usecwait() can be called from user or interrupt context.

SEE ALSO

       delay(9F), timeout(9F), untimeout(9F)

       Writing Device Drivers

NOTES

       The driver wastes processor time by making this call since drv_usecwait() does not block but simply busy-waits. The driver should only make
       calls to  drv_usecwait() as needed, and only for as much time as needed.   drv_usecwait() does not mask out interrupts.

SunOS 5.10							    12 Nov 1992 						  drv_usecwait(9F)