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[PATCH] target/riscv: Use a direct cast for better performance
From: |
Richard W.M. Jones |
Subject: |
[PATCH] target/riscv: Use a direct cast for better performance |
Date: |
Sat, 7 Oct 2023 10:02:28 +0100 |
RISCV_CPU(cs) uses a checked cast. When QOM cast debugging is enabled
this adds about 5% total overhead when emulating RV64 on x86-64 host.
Using a RISC-V guest with 16 vCPUs, 16 GB of guest RAM, virtio-blk
disk. The guest has a copy of the qemu source tree. The test
involves compiling the qemu source tree with 'make clean; time make -j16'.
Before making this change the compile step took 449 & 447 seconds over
two consecutive runs.
After making this change, 428 & 422 seconds.
The saving is about 5%.
Thanks: Paolo Bonzini
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
target/riscv/cpu_helper.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 3a02079290..6174d99fb2 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -66,7 +66,11 @@ void cpu_get_tb_cpu_state(CPURISCVState *env, vaddr *pc,
uint64_t *cs_base, uint32_t *pflags)
{
CPUState *cs = env_cpu(env);
- RISCVCPU *cpu = RISCV_CPU(cs);
+ /*
+ * Using the checked cast RISCV_CPU(cs) imposes ~ 5% overhead when
+ * qemu cast debugging is enabled, so use a direct cast instead.
+ */
+ RISCVCPU *cpu = (RISCVCPU *)cs;
RISCVExtStatus fs, vs;
uint32_t flags = 0;
--
2.41.0
- [PATCH] target/riscv: Use a direct cast for better performance,
Richard W.M. Jones <=