Re: [PATCH v5 0/2] perf: riscv: Preliminary Perf Event Support on RISC-V

[Palmer Dabbelt]

On Tue, 24 Apr 2018 20:19:36 PDT (-0700), alankao@xxxxxxxxxxxxx wrote:
> Hi Atish, Palmer,
>
> On Tue, Apr 24, 2018 at 06:15:49PM -0700, Atish Patra wrote:
> > On 4/24/18 5:29 PM, Palmer Dabbelt wrote:
> > >On Tue, 24 Apr 2018 15:16:16 PDT (-0700), atish.patra@xxxxxxx wrote:
> > >>On 4/24/18 12:44 PM, Palmer Dabbelt wrote:
> > >>>On Tue, 24 Apr 2018 12:27:26 PDT (-0700), atish.patra@xxxxxxx wrote:
> > >>>>On 4/24/18 11:07 AM, Atish Patra wrote:
> > >>>>>On 4/19/18 4:28 PM, Alan Kao wrote:
> > >>>>>However, I got an rcu-stall for the test "47: Event times".
> > >>>>># ./perf test -v 47
> > >>>>Got it working. The test tries to attach the event to CPU0 which doesn't
> > >>>>exist in HighFive Unleashed. Changing it to cpu1 works.
> > >>>>
> > >>>>diff --git a/tools/perf/tests/event-times.c b/tools/perf/tests/event-times.c
> > >>>>index 1a2686f..eb11632f 100644
> > >>>>--- a/tools/perf/tests/event-times.c
> > >>>>+++ b/tools/perf/tests/event-times.c
> > >>>>@@ -113,9 +113,9 @@ static int attach__cpu_disabled(struct perf_evlist
> > >>>>*evlist)
> > >>>>           struct cpu_map *cpus;
> > >>>>           int err;
> > >>>>
> > >>>>-       pr_debug("attaching to CPU 0 as enabled\n");
> > >>>>+       pr_debug("attaching to CPU 1 as disabled\n");
> > >>>>
> > >>>>-       cpus = cpu_map__new("0");
> > >>>>+       cpus = cpu_map__new("1");
> > >>>>           if (cpus == NULL) {
> > >>>>                   pr_debug("failed to call cpu_map__new\n");
> > >>>>                   return -1;
> > >>>>@@ -142,9 +142,9 @@ static int attach__cpu_enabled(struct perf_evlist
> > >>>>*evlist)
> > >>>>           struct cpu_map *cpus;
> > >>>>           int err;
> > >>>>
> > >>>>-       pr_debug("attaching to CPU 0 as enabled\n");
> > >>>>+       pr_debug("attaching to CPU 1 as enabled\n");
> > >>>>
> > >>>>-       cpus = cpu_map__new("0");
> > >>>>+       cpus = cpu_map__new("1");
> > >>>>           if (cpus == NULL) {
> > >>>>                   pr_debug("failed to call cpu_map__new\n");
> > >>>>                   return -1;
> > >>>>
> > >>>>
> > >>>>Palmer,
> > >>>>Would it be better to officially document it somewhere that CPU0 doesn't
> > >>>>exist in the HighFive Unleashed board ?
> > >>>>I fear that there will be other standard tests/code path that may fail
> > >>>>because of inherent assumption of cpu0 presence.
> > >>>
> > >>>I think the best way to fix this is to just have BBL (or whatever the
> > >>>bootloader is) renumber the CPUs so they're contiguous and begin with 0.
> > >>
> > >>Do you mean BBL will update the device tree that kernel eventually parse
> > >>and set the hart id?
> > >>Sounds good to me unless it acts as a big hack in future boot loaders.
> > >
> > >Right now the machine-mode and supervisor-mode hart IDs are logically separate:
> > >the bootloader just provides the hart ID as a register argument when starting
> > >the kernel.
> >
> > Yes.
> >
> >   BBL already needs to enumerate the harts by looking through the
> > >device tree for various other reasons (at least to mask off the harts that
> > >Linux doesn't support), so it's not that much effort to just maintain a mapping
> > >from supervisor-mode hart IDs to machine-mode hart IDs.
> > >
> >
> > But Linux also parses the device tree to get hart ID in
> > riscv_of_processor_hart(). This is used to setup the possible/present cpu
> > map in setup_smp().
> >
> > Thus, Linux also need to see a device tree with cpu0-3 instead of cpu1-4.
> > Otherwise, present cpu map will be incorrect. Isn't it ?
> >
> > >I have some patches floating around that do this, but appear to do it
> > >incorrectly enough that nothing boots so maybe I'm missing something that makes
> > >this complicated :).
> > >
> >
> > Just a wild guess: May be the because of the above reason ;)
>
> Thanks for the test and discussion.  It looks like am implementation issue from
> Unleash, so ... is there anything I should fix and provide a further patch?

You're welcome to fix BBL if you want, but that's unrelated to this patch set.  
I'm going to look over the code again as soon as I get a chance to, thanks for 
submitting the patches!