| Message ID | 20250404152750.332791-3-dbarboza@ventanamicro.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | hw/riscv/virt.c: change default CPU to 'max' | expand |
On 4/4/25 08:27, Daniel Henrique Barboza wrote: > Using 'max' as > default CPU is done by other QEMU archs like aarch64 so we'll be more > compatible with everyone else. This isn't true. qemu-system-aarch64 -M virt defaults to cortex-a15 (for hysterical raisins), which is completely and totally useless. Which means that one must always pass a -cpu option to qemu-system-aarch64. Moreover, -cpu max has zero migration guarantees, so anyone who wants to be able to reliably migrate is encouraged to use a real cpu model. I suppose, for throwaway VMs, -cpu max is a decent default. But there's a lot to be said for not specifying a default at all. r~
diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c index c9d255d8a8..ff7a122bef 100644 --- a/hw/riscv/virt.c +++ b/hw/riscv/virt.c @@ -1920,7 +1920,7 @@ static void virt_machine_class_init(ObjectClass *oc, void *data) mc->desc = "RISC-V VirtIO board"; mc->init = virt_machine_init; mc->max_cpus = VIRT_CPUS_MAX; - mc->default_cpu_type = TYPE_RISCV_CPU_BASE; + mc->default_cpu_type = TYPE_RISCV_CPU_MAX; mc->block_default_type = IF_VIRTIO; mc->no_cdrom = 1; mc->pci_allow_0_address = true;
In [1], minute 44, we have a hint from a Canonical kernel developer that the next Ubuntu LTS will be RVA23 compliant. If this really comes to pass, the 'virt' CPU won't run it by default - we'll need to either use 'rva23s64' or 'max' CPUs instead because rv64 is not RVA23 compliant. Other distros will follow suit eventually, given that RISC-V profiles provides the most stable ABI to build a distro in the RISC-V land. This exposes a long standing issue with the current rv64 CPU: it doesn't represent anything in particular. Extensions were added in it as time went by and we ended up with a CPU that has a random set of extensions. Changing the default 'virt' CPU to 'max' gives users a guarantee that the board will always run with the latest features/profile available in QEMU, which is the intention of most regular users. Using 'max' as default CPU is done by other QEMU archs like aarch64 so we'll be more compatible with everyone else. Note that this change does not affect existing scripts that are using the rv64 CPU, e.g. a command line like "-cpu rv64,v=true" will work the same after this patch. [1] https://fosdem.org/2025/schedule/event/fosdem-2025-6031-risc-v-hardware-where-are-we-/ Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com> --- hw/riscv/virt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)