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[Qemu-devel] [PATCH v8 21/25] target-arm: don't generate WFE/YIELD calls
From: |
Alex Bennée |
Subject: |
[Qemu-devel] [PATCH v8 21/25] target-arm: don't generate WFE/YIELD calls for MTTCG |
Date: |
Fri, 27 Jan 2017 10:39:18 +0000 |
The WFE and YIELD instructions are really only hints and in TCG's case
they were useful to move the scheduling on from one vCPU to the next. In
the parallel context (MTTCG) this just causes an unnecessary cpu_exit
and contention of the BQL.
Signed-off-by: Alex Bennée <address@hidden>
Reviewed-by: Richard Henderson <address@hidden>
---
target/arm/op_helper.c | 7 +++++++
target/arm/translate-a64.c | 8 ++++++--
target/arm/translate.c | 20 ++++++++++++++++----
3 files changed, 29 insertions(+), 6 deletions(-)
diff --git a/target/arm/op_helper.c b/target/arm/op_helper.c
index e1a883c595..abfa7cdd39 100644
--- a/target/arm/op_helper.c
+++ b/target/arm/op_helper.c
@@ -436,6 +436,13 @@ void HELPER(yield)(CPUARMState *env)
ARMCPU *cpu = arm_env_get_cpu(env);
CPUState *cs = CPU(cpu);
+ /* When running in MTTCG we don't generate jumps to the yield and
+ * WFE helpers as it won't affect the scheduling of other vCPUs.
+ * If we wanted to more completely model WFE/SEV so we don't busy
+ * spin unnecessarily we would need to do something more involved.
+ */
+ g_assert(!parallel_cpus);
+
/* This is a non-trappable hint instruction that generally indicates
* that the guest is currently busy-looping. Yield control back to the
* top level loop so that a more deserving VCPU has a chance to run.
diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 88a4df6959..05162f335e 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -1342,10 +1342,14 @@ static void handle_hint(DisasContext *s, uint32_t insn,
s->is_jmp = DISAS_WFI;
return;
case 1: /* YIELD */
- s->is_jmp = DISAS_YIELD;
+ if (!parallel_cpus) {
+ s->is_jmp = DISAS_YIELD;
+ }
return;
case 2: /* WFE */
- s->is_jmp = DISAS_WFE;
+ if (!parallel_cpus) {
+ s->is_jmp = DISAS_WFE;
+ }
return;
case 4: /* SEV */
case 5: /* SEVL */
diff --git a/target/arm/translate.c b/target/arm/translate.c
index dc67887918..444a24c2b6 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -4343,20 +4343,32 @@ static void gen_exception_return(DisasContext *s,
TCGv_i32 pc)
gen_rfe(s, pc, load_cpu_field(spsr));
}
+/*
+ * For WFI we will halt the vCPU until an IRQ. For WFE and YIELD we
+ * only call the helper when running single threaded TCG code to ensure
+ * the next round-robin scheduled vCPU gets a crack. In MTTCG mode we
+ * just skip this instruction. Currently the SEV/SEVL instructions
+ * which are *one* of many ways to wake the CPU from WFE are not
+ * implemented so we can't sleep like WFI does.
+ */
static void gen_nop_hint(DisasContext *s, int val)
{
switch (val) {
case 1: /* yield */
- gen_set_pc_im(s, s->pc);
- s->is_jmp = DISAS_YIELD;
+ if (!parallel_cpus) {
+ gen_set_pc_im(s, s->pc);
+ s->is_jmp = DISAS_YIELD;
+ }
break;
case 3: /* wfi */
gen_set_pc_im(s, s->pc);
s->is_jmp = DISAS_WFI;
break;
case 2: /* wfe */
- gen_set_pc_im(s, s->pc);
- s->is_jmp = DISAS_WFE;
+ if (!parallel_cpus) {
+ gen_set_pc_im(s, s->pc);
+ s->is_jmp = DISAS_WFE;
+ }
break;
case 4: /* sev */
case 5: /* sevl */
--
2.11.0
- [Qemu-devel] [PATCH v8 09/25] tcg: remove global exit_request, (continued)
- [Qemu-devel] [PATCH v8 09/25] tcg: remove global exit_request, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 16/25] cputlb and arm/sparc targets: convert mmuidx flushes from varg to bitmap, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 22/25] target-arm/cpu.h: make ARM_CP defined consistent, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 18/25] cputlb: atomically update tlb fields used by tlb_reset_dirty, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 23/25] target-arm: introduce ARM_CP_EXIT_PC, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 24/25] target-arm: ensure all cross vCPUs TLB flushes complete, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 25/25] tcg: enable MTTCG by default for ARM on x86 hosts, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 21/25] target-arm: don't generate WFE/YIELD calls for MTTCG,
Alex Bennée <=
- [Qemu-devel] [PATCH v8 17/25] cputlb: add tlb_flush_by_mmuidx async routines, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 19/25] cputlb: introduce tlb_flush_*_all_cpus[_synced], Alex Bennée, 2017/01/27
- Re: [Qemu-devel] [PATCH v8 00/25] Remaining MTTCG Base patches and ARM enablement, Pranith Kumar, 2017/01/29
- Re: [Qemu-devel] [PATCH v8 00/25] Remaining MTTCG Base patches and ARM enablement, Richard Henderson, 2017/01/31