| Message ID | 20240415065245.25455-1-yongxuan.wang@sifive.com |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1] target/riscv/kvm.c: Fix the hart bit setting of AIA | expand |
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 > >
Hi Alistair, On Mon, Apr 29, 2024 at 11:25 AM Alistair Francis <alistair23@gmail.com> wrote: > > 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. > Sure! > > > > [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()? > find_last_bit() returns the position of the leftmost set bit. The output will not be 1 when the given input is an odd number. Regards, Yong-Xuan > 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 > > > >
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--; + hart_bits = find_last_bit(&max_hart_per_socket, BITS_PER_LONG) + 1; + } 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);
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. [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(-)