Re: [edk2-devel] [PATCH v7 3/5] MdePkg: Implement RISC-V Cache Management Operations

["Sunil V L" <sunilvl@ventanamicro.com>]

On Mon, Oct 30, 2023 at 10:38:21AM +0100, Laszlo Ersek wrote:
> On 10/29/23 20:12, Pedro Falcato wrote:
> > On Sun, Oct 29, 2023 at 2:46 PM Dhaval Sharma <dhaval@rivosinc.com> wrote:
> >>
> >> Implement Cache Management Operations (CMO) defined by
> >> RISC-V spec https://github.com/riscv/riscv-CMOs.
> >>
> >> Notes:
> >> 1. CMO only supports block based Operations. Meaning cache
> >>    flush/invd/clean Operations are not available for the entire
> >>    range. In that case we fallback on fence.i instructions.
> >> 2. Operations are implemented using Opcodes to make them compiler
> >>    independent. binutils 2.39+ compilers support CMO instructions.
> >>
> >> Test:
> >> 1. Ensured correct instructions are refelecting in asm
> > 
> > nit: reflecting
> > 
> >> 2. Not able to verify actual instruction in HW as Qemu ignores
> >>    any actual cache operations.
> > 
> > Do you have no way to test this in hardware? Since Rivos is a RISCV
> > vendor and all ;)
> > I don't like inviting the idea of merging CPU architectural changes
> > without actually testing them in something resembling real silicon
> > (i.e QEMU KVM is _fine_, QEMU TCG really isn't).
> > 
> 
> Hopefully I'm not drawing an incorrect parallel here, but, as I recall
> arm64 enablement in 2014, nearly all initial enablement in RHEL occurred
> on software emulators (ARM Foundation Model, ARM FVP, then QEMU TCG).
> You need to start somewhere. In particular, qemu-system-aarch64 was a
> huge step forward (performance-wise) once it *existed*, relative to the
> Foundation Model / FVP, even though qemu-system-aarch64 wouldn't emulate
> CPU caches (IIRC).
> 
I agree. As per my knowledge, we don't have a publicly available silicon
implementing these features as of today. So, we are taking the approach
of how linux merged these features when the code adhered to the spec. It
will be great for downstream to get these patches merged.

Thanks,
Sunil


-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#110312): https://edk2.groups.io/g/devel/message/110312
Mute This Topic: https://groups.io/mt/102256466/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-