Re: Proposal v2: SBI PMU Extension

Anup Patel

Based on my previous reply…


To monitor RAW event 0x12345678, user-space perf tool will create user space perf RAW event (i.e. perf_event_attr.type == 4 and perf_event_attr.config = = 0x12345678). The Linux RISC-V PMU driver will allocate and map matching HARDWARE counter which supports specified corrosponding SBI RAW event (event_idx.type = 2, event_idx.code = 0x678 and = 0x12345). Finally, the SBI_PMU_COUNTER_START call implemented by OpenSBI will write 0x12345678 (or some platform specific translated value of 0x12345678) to appropriate mhpmeventX CSR).


(Note: above we assume mhpmcounterX supports monitoring RAW event 0x12345678 and OpenSBI is aware of this)






From: Brian Grayson <brian.grayson@...>
Sent: 09 July 2020 12:35
To: Zong Li <>
Cc: Anup Patel <Anup.Patel@...>; Atish Patra <Atish.Patra@...>; andrew@...; tech-unixplatformspec@...; gfavor@...
Subject: Re: [RISC-V] [tech-unixplatformspec] Proposal v2: SBI PMU Extension


My question is, let's say I know that putting the value 0x12345678 into the mhpmevent3 register gets me the event I want, and there is no support for that event in the SBI spec/API. Will this API allow me to program such an event, basically bypassing the usual mapping functionality? perf basically allows you to say "I know this event number is not one you know about, but it's the value I want placed directly into the hardware." I want to ensure that the full capabilities of the hardware will still be accessible through the SBI spec in some sort of "raw" mode, and I didn't see a way for that to happen right now. We don't want to restrict users to the lowest common denominator of functionality.





On Wed, Jul 8, 2020 at 10:27 PM Zong Li <> wrote:

On Thu, Jul 9, 2020 at 1:06 AM Brian Grayson <brian.grayson@...> wrote:
> Would there be a raw style interface to access all the SBI-unaware events, like perf's rNNN support?

Follow this question, in our current proposal, s-mode software only
knows the event_idx, and m-mode firmware takes care of the mapping, my
question is that s-mode software doesn't seem to understand the
meaning of each event_idx, that means, it just get the array of all
supported event_idx, but couldn't know which one is for what. This
also happened on u-mode program, for rNNN interface, normally, we
should refer to the processor specific documentation for getting these
details, and now, users won't know what value they should give. Please
correct me if I miss something. Thanks.

> How would this work on a multicore system -- would the SBI calls only handle the current hart's counters? That seems easiest to deal with.
> Brian

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