Re: A proposal to enhance RISC-V HPM (Hardware Performance Monitor)


Anup Patel
 

Hi Greg,

 

Few comments on your proposal (https://lists.riscv.org/g/tech-privileged/message/205):

 

1. The BIT[31] is not required because we already have MCOUNTINHIBIT CSR

2. The BIT[28] contradicts CSR number semantics of HPMCOUNTER CSR because currently all HPMCOUNTER CSRs are “User-Read-Only”.

3. We need to align “event_info” definition in SBI PMU Extension to consider your prosed bits in MHPMEVENT CSRs.

 

Regards,

Anup

 

From: tech-privileged@... <tech-privileged@...> On Behalf Of Greg Favor
Sent: 30 July 2020 12:57
To: alankao <alankao@...>
Cc: tech-privileged@...
Subject: Re: [RISC-V] [tech-privileged] A proposal to enhance RISC-V HPM (Hardware Performance Monitor)

 

Alan,

 

I'm fine with taking the lead on this architecture extension.  But it should follow a proper process as directed by the TSC.  Thus far this would mean getting a new TG created or doing something less formally under an existing TG.  But for smaller extension proposals like this there is need for a proper lighter weight and faster process.  Need for this is recognized and I suspect will probably be promulgated by the TSC some time soon.

 

So I suggest we pause for a short bit, and then see if we can follow that expedited process once it is available.  In the meantime I/we can prepare what we can in advance.  (I don't think this will represent a material slow down to getting to a frozen spec and then to ratification.)

 

Greg

 

On Wed, Jul 29, 2020 at 5:24 PM alankao <alankao@...> wrote:

Hi all,

Although there were some non-resolved discussions, it has little to do with what we should do for the next step.  I believe Greg's proposal is superior to the original one in the starting thread because

1.  It reuses `hpmevents` for most of the functions that we all agree that RISC-V needs, instead of adding a bunch of new registers.
2.  It is H-ext-aware

I suggest Greg take the lead to start a PR in the ISA Repo, I can help review and evaluate the effort to patch existing software.

Thanks,
Alan

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