Messages in this thread | | | From | Anup Patel <> | Date | Tue, 30 Jun 2020 15:48:49 +0530 | Subject | Re: [RFC PATCH 0/6] Support raw event and DT for perf on RISC-V |
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On Tue, Jun 30, 2020 at 1:34 PM Zong Li <zong.li@sifive.com> wrote: > > On Tue, Jun 30, 2020 at 3:40 PM Anup Patel <anup@brainfault.org> wrote: > > > > On Tue, Jun 30, 2020 at 12:07 PM Zong Li <zong.li@sifive.com> wrote: > > > > > > On Mon, Jun 29, 2020 at 9:23 PM Anup Patel <anup@brainfault.org> wrote: > > > > > > > > On Mon, Jun 29, 2020 at 6:23 PM Zong Li <zong.li@sifive.com> wrote: > > > > > > > > > > On Mon, Jun 29, 2020 at 4:28 PM Anup Patel <anup@brainfault.org> wrote: > > > > > > > > > > > > On Mon, Jun 29, 2020 at 11:22 AM Zong Li <zong.li@sifive.com> wrote: > > > > > > > > > > > > > > On Mon, Jun 29, 2020 at 12:53 PM Anup Patel <anup@brainfault.org> wrote: > > > > > > > > > > > > > > > > On Mon, Jun 29, 2020 at 8:49 AM Zong Li <zong.li@sifive.com> wrote: > > > > > > > > > > > > > > > > > > This patch set adds raw event support on RISC-V. In addition, we > > > > > > > > > introduce the DT mechanism to make our perf more generic and common. > > > > > > > > > > > > > > > > > > Currently, we set the hardware events by writing the mhpmeventN CSRs, it > > > > > > > > > would raise an illegal instruction exception and trap into m-mode to > > > > > > > > > emulate event selector CSRs access. It doesn't make sense because we > > > > > > > > > shouldn't write the m-mode CSRs in s-mode. Ideally, we should set event > > > > > > > > > selector through standard SBI call or the shadow CSRs of s-mode. We have > > > > > > > > > prepared a proposal of a new SBI extension, called "PMU SBI extension", > > > > > > > > > but we also discussing the feasibility of accessing these PMU CSRs on > > > > > > > > > s-mode at the same time, such as delegation mechanism, so I was > > > > > > > > > wondering if we could use SBI calls first and make the PMU SBI extension > > > > > > > > > as legacy when s-mode access mechanism is accepted by Foundation? or > > > > > > > > > keep the current situation to see what would happen in the future. > > > > > > > > > > > > > > > > > > This patch set also introduces the DT mechanism, we don't want to add too > > > > > > > > > much platform-dependency code in perf like other architectures, so we > > > > > > > > > put the mapping of generic hardware events to DT, then we can easy to > > > > > > > > > transfer generic hardware events to vendor's own hardware events without > > > > > > > > > any platfrom-dependency stuff in our perf. > > > > > > > > > > > > > > > > Please re-write this series to have RISC-V PMU driver as a regular > > > > > > > > platform driver as drivers/perf/riscv_pmu.c. > > > > > > > > > > > > > > > > The PMU related sources will have to be removed from arch/riscv. > > > > > > > > > > > > > > > > Based on implementation of final drivers/perf/riscv_pmu.c we will > > > > > > > > come-up with drivers/perf/riscv_sbi_pmu.c driver for SBI perf counters. > > > > > > > > > > > > > > > > > > > > > > There are some different ways to implement perf, and current > > > > > > > implementation seems to be consensus when perf was introduced at the > > > > > > > beginning [0][1]. I don't persist to which one, I could change the > > > > > > > implementation as you mentioned if it is a new consensus one. > > > > > > > > > > > > > > [0] https://github.com/riscv/riscv-linux/pull/124#issuecomment-367563910 > > > > > > > > > > > > I would not recommend taking the original RISC-V linux fork as reference. > > > > > > > > > > > > Rather we should study how things are done on other architectures. > > > > > > > > > > > > I really appreciate the attempt to make RISC-V PMU driver depend on DT > > > > > > but if we are going this route then we should maximize the use of Linux > > > > > > platform driver framework. In fact, whenever possible we should integrate > > > > > > RISC-V features as platform drivers under the drivers/ directory. > > > > > > > > > > > > > > > > OK, I would change the implementation to platform driver if there is no > > > > > other voice. > > > > > > > > > > > I thought about SBI PMU counters as well. In future, we can easily > > > > > > expose SBI PMU counters as RAW events in the same RISC-V PMU > > > > > > driver. The sbi_probe_extension() can be used in RISC-V PMU driver > > > > > > to check for SBI PMU counters so no special provisions needed in DT > > > > > > for SBI PMU counters. > > > > > > > > > > > > > > > > I thought about probing raw events by SBI extension too, I'm interested if you > > > > > have more detail about this. > > > > > > > > > > It seems to me that it is a little bit hard to return all events > > > > > through one SBI call, > > > > > so I thought we could map the generic hardware events and maintain their own > > > > > raw events by each platform in OpenSBI. But eventually, I thought the > > > > > DT mechanism > > > > > is more clear and easy than that. Let me know if you have any ideas about > > > > > probe function. Thanks. > > > > > > > > We can design SBI calls such that no SBI call is required to read > > > > the perf counter. > > > > > > > > The sbi_probe_extension() will only be used to check whether > > > > underlying SBI implementation supports SBI PMU extension. > > > > > > > > As-per my initial thoughts, we can potentially have the following SBI calls: > > > > > > > > 1. SBI_PMU_NUM_COUNTERS > > > > This call will return the number of SBI PMU counters > > > > 2. SBI_PMU_COUNTER_DESCRIBE > > > > This call takes two parameters: 1) physical address 2) counter index > > > > It will write the description of SBI PMU counter at specified > > > > physical address. > > > > The details of the SBI PMU counter will include name, type, etc > > > > > > The main things are that we need to pass the information of raw events > > > and the information of mapping of generic hardware events. Maybe > > > this information could be passed by this SBI call. > > > > > > > 3. SBI_PMU_COUNTER_START > > > > This call takes two parameters: 1) physical address 2) counter index > > > > It will inform SBI implementation to start counting specified counter on the > > > > calling HART. The counter value will be written to the specified physical > > > > address whenever it changes. > > > > > > I would prefer to read the counter directly on s-mode. Spec already defines the > > > mechanism to allow that. But this way would still work if we couldn't > > > read counters > > > on s-mode. > > > > The SBI PMU counters have nothing to do with RISC-V PMU counters because > > these are counters provided by SBI implementation. > > > > All-in-all, we have three types of counters: > > 1. PMU counters defined by RISC-V privilege spec. These are TIME, > > INSRET, and CYCLE CSRs. > > 2. Implementation specific counters accessed via HPMCOUNTER CSRs. > > 3. SBI PMU counters for traps taken and processed by M-mode runtime > > firmware. Examples: number of misaligned load/store, number of illegal > > instructions, number of SBI RFENCE calls, number of SBI IPI calls, etc. > > > > The DT based RISC-V PMU platform driver being discussed in this email > > thread only addresses points 1) and 2) above. > > > > OK, sounds good, I misunderstood your ideas, I mixed the 2) and 3) > and see them as the same thing. Many thanks for the clear explanation.
Cool, we are on the same page till here.
> > > For point 3) above, we need to first define SBI PMU extension. Once SBI > > PMU extension is defined, we can have separate SBI PMU driver in Linux > > or extend RISC-V PMU driver to register additonal counters based on > > SBI PMU extension. > > > > I never suggested to access RISC-V HPMCOUNTER CSRs via SBI calls > > so DT based RISC-V PMU platform driver (for 1) and 2) above) is good > > to have. The SBI PMU extension is a separate topic. > > > > > > > > > 4. SBI_PMU_COUNTER_STOP > > > > This call takes one parameter: 1) counter index > > > > It will inform SBI implementation to stop counting specified counters on > > > > the calling HART. > > > > > > > > The above calls are generic enough to support any number of counters > > > > and we don't need any SBI call to read the counter. We can also assume > > > > all counters to be of fixed 64bit width. In fact, even Hypervisors can support > > > > it's own SBI PMU counters with SBI PMU extension. > > > > > > > > We still need to think more about the above calls because above SBI > > > > calls are just initial ideas. > > > > > > > > > > We also need a SBI call to set the event selector to specify which event > > > is monitored. > > > > SBI_PMU_COUNTER_START will do that. > > I'm not sure whether this SBI call is only for SBI PMU counter and > it's own events. > For 2), it needs one SBI call to set the events, we just set the event selector > by writing m-mode CSRs on s-mode now. If this SBI call could serve 2) > and 3) both, > we don't need another SBI call.
Can you elaborate more ??
Is the SBI call for 2) needed to enable/disable counters in MCOUNTEREN CSR ?
Currently, OpenSBI enables all counters by default but I see the need to enable/disable HPMCOUNTER on-demand from perf event start/stop.
I hope we don't need any other implementation specific CSR to be programmed for enabling/disabling counters on SiFive Unleashed ??
Regards, Anup
> > > > > > > > > > Maybe you can refine the above ideas and send a proposal to the > > > > UnixPlatformSpec mailing list ?? > > > > > > > > > > Ok, let us talk about the details in that. > > > > Regards, > > Anup > > > > > > > > > > > > Regards, > > > > Anup > > > > > > > > > > > > > > > Also, the RISC-V PMU driver can be implemented such that it will > > > > > > work for RV32, RV64, NoMMU RV32, and NoMMU RV64. > > > > > > > > > > > > Regards, > > > > > > Anup > > > > > > > > > > > > > [1] https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/f19TmCNP6yA > > > > > > > > > > > > > > > Regards, > > > > > > > > Anup > > > > > > > > > > > > > > > > > > > > > > > > > > Zong Li (6): > > > > > > > > > dt-bindings: riscv: Add YAML documentation for PMU > > > > > > > > > riscv: dts: sifive: Add DT support for PMU > > > > > > > > > riscv: add definition of hpmcounter CSRs > > > > > > > > > riscv: perf: Add raw event support > > > > > > > > > riscv: perf: introduce DT mechanism > > > > > > > > > riscv: remove PMU menu of Kconfig > > > > > > > > > > > > > > > > > > .../devicetree/bindings/riscv/pmu.yaml | 59 +++ > > > > > > > > > arch/riscv/Kconfig | 13 - > > > > > > > > > arch/riscv/boot/dts/sifive/fu540-c000.dtsi | 13 + > > > > > > > > > arch/riscv/include/asm/csr.h | 58 +++ > > > > > > > > > arch/riscv/include/asm/perf_event.h | 100 ++-- > > > > > > > > > arch/riscv/kernel/Makefile | 2 +- > > > > > > > > > arch/riscv/kernel/perf_event.c | 471 +++++++++++------- > > > > > > > > > 7 files changed, 471 insertions(+), 245 deletions(-) > > > > > > > > > create mode 100644 Documentation/devicetree/bindings/riscv/pmu.yaml > > > > > > > > > > > > > > > > > > -- > > > > > > > > > 2.27.0 > > > > > > > > >
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