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openrisc: sleep instead of spin on secondary wait 

Currently we do a spin on secondary cpus when waiting to boot.  This
theoretically causes issues with power consumption and does cause issues
with qemu cycle burning (it starves cpu 0 from actually being able to
boot.)

This change puts each secondary cpu to sleep if they have a power
management unit, then signals them to wake via IPI when its time to boot.
If the cpus have no power management unit they will loop as before.

Note: The wakeup IPI requires a special interrupt handler as on secondary
cpu's the interrupt infrastructure is not yet established.  This
interrupt handler is set and reset by updating SPR_EVBAR.

Signed-off-by: Stafford Horne <shorne@gmail.com>
This commit is contained in:
Stafford Horne 2017-06-24 07:09:59 +09:00
parent b441aab7aa
commit c056718464
2 changed files with 54 additions and 2 deletions
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51
arch/openrisc/kernel/head.S
View File

@ -712,9 +712,45 @@ _flush_tlb:
#ifdef CONFIG_SMP
secondary_wait:
/* Doze the cpu until we are asked to run */
/* If we dont have power management skip doze */
l.mfspr r25,r0,SPR_UPR
l.andi r25,r25,SPR_UPR_PMP
l.sfeq r25,r0
l.bf secondary_check_release
l.nop
/* Setup special secondary exception handler */
LOAD_SYMBOL_2_GPR(r3, _secondary_evbar)
tophys(r25,r3)
l.mtspr r0,r25,SPR_EVBAR
/* Enable Interrupts */
l.mfspr r25,r0,SPR_SR
l.ori r25,r25,SPR_SR_IEE
l.mtspr r0,r25,SPR_SR
/* Unmask interrupts interrupts */
l.mfspr r25,r0,SPR_PICMR
l.ori r25,r25,0xffff
l.mtspr r0,r25,SPR_PICMR
/* Doze */
l.mfspr r25,r0,SPR_PMR
LOAD_SYMBOL_2_GPR(r3, SPR_PMR_DME)
l.or r25,r25,r3
l.mtspr r0,r25,SPR_PMR
/* Wakeup - Restore exception handler */
l.mtspr r0,r0,SPR_EVBAR
secondary_check_release:
/*
* Check if we actually got the release signal, if not go-back to
* sleep.
*/
l.mfspr r25,r0,SPR_COREID
l.movhi r3,hi(secondary_release)
l.ori r3,r3,lo(secondary_release)
LOAD_SYMBOL_2_GPR(r3, secondary_release)
tophys(r4, r3)
l.lwz r3,0(r4)
l.sfeq r25,r3
@ -1663,6 +1699,17 @@ ENTRY(_early_uart_init)
l.jr r9
l.nop
.align 0x1000
.global _secondary_evbar
_secondary_evbar:
.space 0x800
/* Just disable interrupts and Return */
l.ori r3,r0,SPR_SR_SM
l.mtspr r0,r3,SPR_ESR_BASE
l.rfe
.section .rodata
_string_unhandled_exception:
.string "\n\rRunarunaround: Unhandled exception 0x\0"

5
arch/openrisc/kernel/smp.c
View File

@ -26,6 +26,7 @@ unsigned long secondary_release = -1;
struct thread_info *secondary_thread_info;
enum ipi_msg_type {
IPI_WAKEUP,
IPI_RESCHEDULE,
IPI_CALL_FUNC,
IPI_CALL_FUNC_SINGLE,
@ -42,6 +43,7 @@ static void boot_secondary(unsigned int cpu, struct task_struct *idle)
spin_lock(&boot_lock);
secondary_release = cpu;
smp_cross_call(cpumask_of(cpu), IPI_WAKEUP);
/*
* now the secondary core is starting up let it run its
@ -140,6 +142,9 @@ void handle_IPI(unsigned int ipi_msg)
unsigned int cpu = smp_processor_id();
switch (ipi_msg) {
case IPI_WAKEUP:
break;
case IPI_RESCHEDULE:
scheduler_ipi();
break;