Is RISC-V Static Call worth implementing ?

[Samuel Holland]

On 2024-09-13 3:55 PM, Conor Dooley wrote:
> On Fri, Sep 13, 2024 at 03:05:33AM -0500, Juhan Jin wrote:
>> Hi folks,
>>
>> I’m interested in implementing Static Call for RISC-V, and I want to
>> know whether it is worth the efforts to implement Static Call for
>> RISC-V.
>>
>> Does the aforementioned benefits merit a RISC-V static call implementation 
>> (especially inline)? Or are the benefits so negligible that it’s simply not 
>> worth the effort to do a RISC-V implementation?
> 
> Pretty sure we've talked about wanting it before - Samuel, Alex, Drew
> Jones or Palmer might remember best what exactly we wanted it for
> however, as I do not.

If I remember correctly, we had discussed it in the context of non-coherent DMA
operations, but we decided that the benefit was negligible for that use case.

There are other places that could likely benefit from static calls, such as
Sv39/Sv48/Sv57 differences, some users of riscv_has_extension_*(), or maybe some
hot indirect SBI functions like sbi_set_timer(). But it depends on the overhead.

Regards,
Samuel