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powerpc/64s: Idle POWER8 avoid full state loss recovery where possible

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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>
This commit is contained in:
Nicholas Piggin
2017-04-19 23:05:50 +10:00
committed by Michael Ellerman
parent e420249d44
commit 0d7720a242
2 changed files with 112 additions and 9 deletions
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89
arch/powerpc/kernel/idle_book3s.S
View File

@@ -210,15 +210,20 @@ pnv_enter_arch207_idle_mode:
/* Sleep or winkle */
lbz r7,PACA_THREAD_MASK(r13)
ld r14,PACA_CORE_IDLE_STATE_PTR(r13)
li r5,0
beq cr3,3f
lis r5,PNV_CORE_IDLE_WINKLE_COUNT@h
3:
lwarx_loop1:
lwarx r15,0,r14
andis. r9,r15,PNV_CORE_IDLE_LOCK_BIT@h
bnel- core_idle_lock_held
add r15,r15,r5 /* Add if winkle */
andc r15,r15,r7 /* Clear thread bit */
andi. r15,r15,PNV_CORE_IDLE_THREAD_BITS
andi. r9,r15,PNV_CORE_IDLE_THREAD_BITS
/*
* If cr0 = 0, then current thread is the last thread of the core entering
@@ -509,14 +514,13 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_POWER9_DD1)
pnv_restore_hyp_resource_arch207:
/*
* POWER ISA 2.07 or less.
* Check if we slept with winkle.
* Check if we slept with sleep or winkle.
*/
ld r2,PACATOC(r13);
lbz r0,PACA_THREAD_IDLE_STATE(r13)
cmpwi cr2,r0,PNV_THREAD_NAP
cmpwi cr4,r0,PNV_THREAD_WINKLE
bgt cr2,pnv_wakeup_tb_loss /* Either sleep or Winkle */
lbz r4,PACA_THREAD_IDLE_STATE(r13)
cmpwi cr2,r4,PNV_THREAD_NAP
bgt cr2,pnv_wakeup_tb_loss /* Either sleep or Winkle */
/*
* We fall through here if PACA_THREAD_IDLE_STATE shows we are waking
@@ -535,7 +539,12 @@ pnv_restore_hyp_resource_arch207:
*
* r13 - PACA
* cr3 - gt if waking up with partial/complete hypervisor state loss
*
* If ISA300:
* cr4 - gt or eq if waking up from complete hypervisor state loss.
*
* If ISA207:
* r4 - PACA_THREAD_IDLE_STATE
*/
pnv_wakeup_tb_loss:
ld r1,PACAR1(r13)
@@ -550,6 +559,7 @@ pnv_wakeup_tb_loss:
* is required to return back to reset vector after hypervisor state
* restore is complete.
*/
mr r18,r4
mflr r17
mfspr r16,SPRN_SRR1
BEGIN_FTR_SECTION
@@ -585,10 +595,77 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
* At this stage
* cr2 - eq if first thread to wakeup in core
* cr3- gt if waking up with partial/complete hypervisor state loss
* ISA300:
* cr4 - gt or eq if waking up from complete hypervisor state loss.
*/
BEGIN_FTR_SECTION
/*
* Were we in winkle?
* If yes, check if all threads were in winkle, decrement our
* winkle count, set all thread winkle bits if all were in winkle.
* Check if our thread has a winkle bit set, and set cr4 accordingly
* (to match ISA300, above). Pseudo-code for core idle state
* transitions for ISA207 is as follows (everything happens atomically
* due to store conditional and/or lock bit):
*
* nap_idle() { }
* nap_wake() { }
*
* sleep_idle()
* {
* core_idle_state &= ~thread_in_core
* }
*
* sleep_wake()
* {
* bool first_in_core, first_in_subcore;
*
* first_in_core = (core_idle_state & IDLE_THREAD_BITS) == 0;
* first_in_subcore = (core_idle_state & SUBCORE_SIBLING_MASK) == 0;
*
* core_idle_state |= thread_in_core;
* }
*
* winkle_idle()
* {
* core_idle_state &= ~thread_in_core;
* core_idle_state += 1 << WINKLE_COUNT_SHIFT;
* }
*
* winkle_wake()
* {
* bool first_in_core, first_in_subcore, winkle_state_lost;
*
* first_in_core = (core_idle_state & IDLE_THREAD_BITS) == 0;
* first_in_subcore = (core_idle_state & SUBCORE_SIBLING_MASK) == 0;
*
* core_idle_state |= thread_in_core;
*
* if ((core_idle_state & WINKLE_MASK) == (8 << WINKLE_COUNT_SIHFT))
* core_idle_state |= THREAD_WINKLE_BITS;
* core_idle_state -= 1 << WINKLE_COUNT_SHIFT;
*
* winkle_state_lost = core_idle_state &
* (thread_in_core << WINKLE_THREAD_SHIFT);
* core_idle_state &= ~(thread_in_core << WINKLE_THREAD_SHIFT);
* }
*
*/
cmpwi r18,PNV_THREAD_WINKLE
bne 2f
andis. r9,r15,PNV_CORE_IDLE_WINKLE_COUNT_ALL_BIT@h
subis r15,r15,PNV_CORE_IDLE_WINKLE_COUNT@h
beq 2f
ori r15,r15,PNV_CORE_IDLE_THREAD_WINKLE_BITS /* all were winkle */
2:
/* Shift thread bit to winkle mask, then test if this thread is set,
* and remove it from the winkle bits */
slwi r8,r7,8
and r8,r8,r15
andc r15,r15,r8
cmpwi cr4,r8,1 /* cr4 will be gt if our bit is set, lt if not */
lbz r4,PACA_SUBCORE_SIBLING_MASK(r13)
and r4,r4,r15
cmpwi r4,0 /* Check if first in subcore */