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

[Alan Kao]

On Wed, Apr 25, 2018 at 09:39:04AM -0700, Palmer Dabbelt wrote:
> 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!

Any updates?