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

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Date:   Wed, 25 Apr 2018 11:19:36 +0800
From:   Alan Kao <alankao@...estech.com>
To:     Atish Patra <atish.patra@....com>
CC:     Palmer Dabbelt <palmer@...ive.com>,
        "albert@...ive.com" <albert@...ive.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "sols@...ive.com" <sols@...ive.com>,
        "corbet@....net" <corbet@....net>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "greentime@...estech.com" <greentime@...estech.com>,
        "nickhu@...estech.com" <nickhu@...estech.com>
Subject: Re: [PATCH v5 0/2] perf: riscv: Preliminary Perf Event Support on
 RISC-V

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@....com wrote:
> >>On 4/24/18 12:44 PM, Palmer Dabbelt wrote:
> >>>On Tue, 24 Apr 2018 12:27:26 PDT (-0700), atish.patra@....com 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?