Revision 3a53396b0381ec9d5180fd8fe7a681c8ce95fd9a authored by ShuoX Liu on 28 March 2012, 22:19:11 UTC, committed by Len Brown on 30 March 2012, 05:52:58 UTC
Some C states of new CPU might be not good. One reason is BIOS might configure them incorrectly. To help developers root cause it quickly, the patch adds a new sysfs entry, so developers could disable specific C state manually. In addition, C state might have much impact on performance tuning, as it takes much time to enter/exit C states, which might delay interrupt processing. With the new debug option, developers could check if a deep C state could impact performance and how much impact it could cause. Also add this option in Documentation/cpuidle/sysfs.txt. [akpm@linux-foundation.org: check kstrtol return value] Signed-off-by: ShuoX Liu <shuox.liu@intel.com> Reviewed-by: Yanmin Zhang <yanmin_zhang@intel.com> Reviewed-and-Tested-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Len Brown <len.brown@intel.com>
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Kconfig.preempt
choice
prompt "Preemption Model"
default PREEMPT_NONE
config PREEMPT_NONE
bool "No Forced Preemption (Server)"
help
This is the traditional Linux preemption model, geared towards
throughput. It will still provide good latencies most of the
time, but there are no guarantees and occasional longer delays
are possible.
Select this option if you are building a kernel for a server or
scientific/computation system, or if you want to maximize the
raw processing power of the kernel, irrespective of scheduling
latencies.
config PREEMPT_VOLUNTARY
bool "Voluntary Kernel Preemption (Desktop)"
help
This option reduces the latency of the kernel by adding more
"explicit preemption points" to the kernel code. These new
preemption points have been selected to reduce the maximum
latency of rescheduling, providing faster application reactions,
at the cost of slightly lower throughput.
This allows reaction to interactive events by allowing a
low priority process to voluntarily preempt itself even if it
is in kernel mode executing a system call. This allows
applications to run more 'smoothly' even when the system is
under load.
Select this if you are building a kernel for a desktop system.
config PREEMPT
bool "Preemptible Kernel (Low-Latency Desktop)"
select PREEMPT_COUNT
help
This option reduces the latency of the kernel by making
all kernel code (that is not executing in a critical section)
preemptible. This allows reaction to interactive events by
permitting a low priority process to be preempted involuntarily
even if it is in kernel mode executing a system call and would
otherwise not be about to reach a natural preemption point.
This allows applications to run more 'smoothly' even when the
system is under load, at the cost of slightly lower throughput
and a slight runtime overhead to kernel code.
Select this if you are building a kernel for a desktop or
embedded system with latency requirements in the milliseconds
range.
endchoice
config PREEMPT_COUNT
bool
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