diff options
| author | Nicholas Piggin <npiggin@gmail.com> | 2017-04-19 23:05:50 +1000 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2017-04-23 20:32:12 +1000 |
| commit | 0d7720a24234cefa8b318b1a3cf0b302a51faec9 (patch) | |
| tree | 8876c07f27927d3290451a9b9795d63423ce8099 /arch/powerpc/include/asm/cpuidle.h | |
| parent | e420249d44d02e9fc110087ed8feddc38b13528c (diff) | |
powerpc/64s: Idle POWER8 avoid full state loss recovery where possible
If not all threads were in winkle, full state loss recovery is not
necessary and can be avoided. A previous patch removed this optimisation
due to some complexity with the implementation. Re-implement it by
counting the number of threads in winkle with the per-core idle state.
Only restore full state loss if all threads were in winkle.
This has a small window of false positives right before threads execute
winkle and just after they wake up, when the winkle count does not
reflect the true number of threads in winkle. This is not a significant
problem in comparison with even the minimum winkle duration. For
correctness, a false positive is not a problem (only false negatives
would be).
Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/include/asm/cpuidle.h')
| -rw-r--r-- | arch/powerpc/include/asm/cpuidle.h | 32 |
1 files changed, 29 insertions, 3 deletions
diff --git a/arch/powerpc/include/asm/cpuidle.h b/arch/powerpc/include/asm/cpuidle.h index dd6a63f0a10f..52586f9956bb 100644 --- a/arch/powerpc/include/asm/cpuidle.h +++ b/arch/powerpc/include/asm/cpuidle.h @@ -2,13 +2,39 @@ #define _ASM_POWERPC_CPUIDLE_H #ifdef CONFIG_PPC_POWERNV -/* Used in powernv idle state management */ +/* Thread state used in powernv idle state management */ #define PNV_THREAD_RUNNING 0 #define PNV_THREAD_NAP 1 #define PNV_THREAD_SLEEP 2 #define PNV_THREAD_WINKLE 3 -#define PNV_CORE_IDLE_LOCK_BIT 0x10000000 -#define PNV_CORE_IDLE_THREAD_BITS 0x000000FF + +/* + * Core state used in powernv idle for POWER8. + * + * The lock bit synchronizes updates to the state, as well as parts of the + * sleep/wake code (see kernel/idle_book3s.S). + * + * Bottom 8 bits track the idle state of each thread. Bit is cleared before + * the thread executes an idle instruction (nap/sleep/winkle). + * + * Then there is winkle tracking. A core does not lose complete state + * until every thread is in winkle. So the winkle count field counts the + * number of threads in winkle (small window of false positives is okay + * around the sleep/wake, so long as there are no false negatives). + * + * When the winkle count reaches 8 (the COUNT_ALL_BIT becomes set), then + * the THREAD_WINKLE_BITS are set, which indicate which threads have not + * yet woken from the winkle state. + */ +#define PNV_CORE_IDLE_LOCK_BIT 0x10000000 + +#define PNV_CORE_IDLE_WINKLE_COUNT 0x00010000 +#define PNV_CORE_IDLE_WINKLE_COUNT_ALL_BIT 0x00080000 +#define PNV_CORE_IDLE_WINKLE_COUNT_BITS 0x000F0000 +#define PNV_CORE_IDLE_THREAD_WINKLE_BITS_SHIFT 8 +#define PNV_CORE_IDLE_THREAD_WINKLE_BITS 0x0000FF00 + +#define PNV_CORE_IDLE_THREAD_BITS 0x000000FF /* * ============================ NOTE ================================= |