diff options
| author | Alex Bennée <alex.bennee@linaro.org> | 2017-02-23 18:29:24 +0000 |
|---|---|---|
| committer | Alex Bennée <alex.bennee@linaro.org> | 2017-02-24 10:32:46 +0000 |
| commit | c22edfebff29f63d793032e4fbd42a035bb73e27 (patch) | |
| tree | 044ff53d9b0d2b90df07e228e619b9d8f2513ae7 /target/arm/op_helper.c | |
| parent | 062ba099e01ff1474be98c0a4f3da351efab5d9d (diff) | |
target-arm: don't generate WFE/YIELD calls for MTTCG
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 <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Diffstat (limited to 'target/arm/op_helper.c')
| -rw-r--r-- | target/arm/op_helper.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/target/arm/op_helper.c b/target/arm/op_helper.c index 5f3e3bdae2..d64c8670fa 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. |