IBM Power7 Optimization And Tuning Manual page 65

Where:
op: Operation. Possible values are DSCR_WRITE, DSCR_READ, DSCR_GET_PROPERTIES, and
DSCR_SET_DEFAULT.
Buf_p: Pointer to an area of memory where the values are copied from (DSCR_WRITE) or
copied to (DSCR_READ and DSCR_GET_PROPERTIES). For DSCR_WRITE, DSCR_READ, and
DSCR_SET_DEFAULT operations, buf_p must be a pointer to a 64-bit data area (long
long *). For DSCR_GET_PROPERTIES, buf_p must be a pointer to a struct
dscr_properties (defined in <sys/machine.h>).
Size in bytes of the area pointed to by buf_p.
Size:
Function:
The action that is taken depends on the value of the operation parameter that is defined
in <sys/machine.h>:
DSCR_WRITE
DSCR_READ
DSCR_GET_PROPERTIES
DSCR_SET_DEFAULT
Return values are:
0 if successful
-1 if an error detected. In this case, errno is set to indicate the error. Possible values are:
EINVAL Invalid value for DSCR (DSCR_WRITE, DSCR_SET_DEFAULT).
Invalid address that is passed to function.
EFAULT
EPERM Operation not permitted (DSCR_SET_DEFAULT by non-root user).
ENOTSUP Data streams that are not supported by platform hardware.
Symbolic values for the following SSE and DPFD fields are defined in <sys/machine.h>:
DPFD_DEFAULT 0
1
DPFD_NONE
DPFD_SHALLOWEST 2
DPFD_SHALLOW 3
Stores a new value from the input buffer into the process
context and in the DSCR.
Reads the current value of DSCR and returns it in the
output buffer.
Reads the number of hardware streams that are supported
by the platform, the platform (firmware) default Prefetch
Depth and the Operating System default Prefetch Depth from
kernel memory, and returns the values in the output buffer
(struct dscr_properties defined in <sys/machine.h>).
Sets a 64-bit DSCR value in a buffer pointed to by buf_p as
the operating system default. Returns the old default in the
buffer pointed to by buf_p. Requires root authority. The new
default value is used by all the processes that do not
explicitly set a DSCR value using DSCR_WRITE. The new
default is not permanent across reboots. For an operating
system default prefetch depth that is permanent across
reboots, use the dscrctl command, which adds an entry into
the inittab to initialize the system-wide prefetch depth default
value upon reboot (for a description of this command, see
"The dscrctl command" on page 50).
Chapter 2. The POWER7 processor
49