From: Alistair Francis <alistair23@gmail.com>
To: Yong-Xuan Wang <yongxuan.wang@sifive.com>
Cc: qemu-devel@nongnu.org, qemu-riscv@nongnu.org,
greentime.hu@sifive.com, vincent.chen@sifive.com,
frank.chang@sifive.com, jim.shu@sifive.com,
"Palmer Dabbelt" <palmer@dabbelt.com>,
"Alistair Francis" <alistair.francis@wdc.com>,
"Bin Meng" <bin.meng@windriver.com>,
"Weiwei Li" <liwei1518@gmail.com>,
"Daniel Henrique Barboza" <dbarboza@ventanamicro.com>,
"Liu Zhiwei" <zhiwei_liu@linux.alibaba.com>,
"Andrew Jones" <ajones@ventanamicro.com>,
"Philippe Mathieu-Daudé" <philmd@linaro.org>
Subject: Re: [PATCH 1/1] target/riscv/kvm.c: Fix the hart bit setting of AIA
Date: Mon, 29 Apr 2024 13:25:11 +1000 [thread overview]
Message-ID: <CAKmqyKO3qj9k74RBp+KCGxgPR_=ZGCSzdUDdGrQj9TPJCUD1Nw@mail.gmail.com> (raw)
In-Reply-To: <20240415065245.25455-1-yongxuan.wang@sifive.com>
On Mon, Apr 15, 2024 at 4:53 PM Yong-Xuan Wang <yongxuan.wang@sifive.com> wrote:
>
> The hart bit setting is different with Linux AIA driver[1] when the number
> of hart is power of 2. For example, when the guest has 4 harts, the
> estimated result of AIA driver is 2, whereas we pass 3 to RISC-V/KVM. Since
> only 2 bits are needed to represent 4 harts, update the formula to get the
> accurate result.
I don't really follow this.
Do you mind re-wording it to talk about what the specification says?
Not what Linux does.
>
> [1] https://lore.kernel.org/all/20240307140307.646078-1-apatel@ventanamicro.com/
>
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
> ---
> target/riscv/kvm/kvm-cpu.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index 6a6c6cae80f1..388c4ddaa145 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -1642,7 +1642,14 @@ void kvm_riscv_aia_create(MachineState *machine, uint64_t group_shift,
> }
> }
>
> - hart_bits = find_last_bit(&max_hart_per_socket, BITS_PER_LONG) + 1;
> +
> + if (max_hart_per_socket > 1) {
> + max_hart_per_socket--;
Assuming there are an even number of cores (which there usually are)
won't this always result in a
> + hart_bits = find_last_bit(&max_hart_per_socket, BITS_PER_LONG) + 1;
1 being returned by find_last_bit()?
Alistair
> + } else {
> + hart_bits = 0;
> + }
> +
> ret = kvm_device_access(aia_fd, KVM_DEV_RISCV_AIA_GRP_CONFIG,
> KVM_DEV_RISCV_AIA_CONFIG_HART_BITS,
> &hart_bits, true, NULL);
> --
> 2.17.1
>
>
next prev parent reply other threads:[~2024-04-29 3:26 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-15 6:52 [PATCH 1/1] target/riscv/kvm.c: Fix the hart bit setting of AIA Yong-Xuan Wang
2024-04-29 3:25 ` Alistair Francis [this message]
2024-05-07 10:12 ` Yong-Xuan Wang
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