Re: [PATCH v3] target/riscv: Use env_archcpu for better performance

[Alistair Francis <alistair23@gmail.com>]

On Mon, Oct 9, 2023 at 10:50 PM Richard W.M. Jones <rjones@redhat.com> wrote:
>
> 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 & 421 seconds.
>
> The saving is over 5%.
>
> Thanks: Paolo Bonzini
> Thanks: Philippe Mathieu-Daudé
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu_helper.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 3a02079290..8c28241c18 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -65,8 +65,7 @@ int riscv_cpu_mmu_index(CPURISCVState *env, bool ifetch)
>  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);
> +    RISCVCPU *cpu = env_archcpu(env);
>      RISCVExtStatus fs, vs;
>      uint32_t flags = 0;
>
> --
> 2.41.0
>
>