linux-kernel - Re: [PATCH 2/3] tools/power turbostat: avoid an infinite loop of restarts

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Message-ID: <10b3298c-99ab-4567-a793-9f12fa7f1dd0@redhat.com>
Date: Mon, 1 Dec 2025 07:18:36 -0500
From: David Arcari <darcari@...hat.com>
To: Len Brown <lenb@...nel.org>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] tools/power turbostat: avoid an infinite loop of
 restarts


I'll take a look with that in mind, but this is really a second order 
issue and could be deferred until a latter date.  It's patches 1 and 3 
that resolve the main issue and should be resolved more quickly.

-DA

On 11/27/25 12:45 PM, Len Brown wrote:
> I guess it is sort of an art form upon malfunction to decide whether
> it is fatal or not.
> 
> I suppose if we know that a counter used to work, and it stops working, then we
> are responding to a configuration change.  We don't want to count a
> certain number
> of configuration changes as a fatal error.
> 
> A more useful heuristic may be to recognize when there are failures
> without any intervening successes,
> and if those happen many times per second.  Likely that is the
> infinite loop case we're looking for...
> 
> On Tue, Nov 25, 2025 at 4:51 PM David Arcari <darcari@...hat.com> wrote:
>>
>>
>> I see.  Perhaps this isn't fixable then.  I'll take another look.
>>
>> -DA
>>
>> On 11/25/25 2:12 PM, Len Brown wrote:
>>> this patch introduces a limit of 10-restarts per turbostat lifetime,
>>> down from infinity.
>>>
>>> some turbostat invocations span multiple uses of cpu online/offline --
>>> so this limit will not fly.
>>>
>>> On Tue, Nov 18, 2025 at 10:58 AM David Arcari <darcari@...hat.com> wrote:
>>>>
>>>> There are some error cases where turbostat will attempt to reinitialize
>>>> by calling the re_initialize() function.  The code attempts to avoid
>>>> an infinite loop by checking the value of 'restarted' in one case, but
>>>> not others. It should be checked in all cases of restart.  Additonally,
>>>> the 'restarted' is reset to zero at the start of the loop which also
>>>> needs to be removed.
>>>>
>>>> Signed-off-by: David Arcari <darcari@...hat.com>
>>>> Cc: Len Brown <lenb@...nel.org>
>>>> Cc: linux-kernel@...r.kernel.org
>>>> ---
>>>>    tools/power/x86/turbostat/turbostat.c | 10 +++++-----
>>>>    1 file changed, 5 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
>>>> index 584b0f7f9067..5567b9ecd516 100644
>>>> --- a/tools/power/x86/turbostat/turbostat.c
>>>> +++ b/tools/power/x86/turbostat/turbostat.c
>>>> @@ -6722,7 +6722,11 @@ void turbostat_loop()
>>>>           set_my_sched_priority(-20);
>>>>
>>>>    restart:
>>>> -       restarted++;
>>>> +       if (restarted++ > 10) {
>>>> +               if (!retval)
>>>> +                       retval = -1;
>>>> +               exit(retval);
>>>> +       }
>>>>
>>>>           snapshot_proc_sysfs_files();
>>>>           retval = for_all_cpus(get_counters, EVEN_COUNTERS);
>>>> @@ -6730,13 +6734,9 @@ void turbostat_loop()
>>>>           if (retval < -1) {
>>>>                   exit(retval);
>>>>           } else if (retval == -1) {
>>>> -               if (restarted > 10) {
>>>> -                       exit(retval);
>>>> -               }
>>>>                   re_initialize();
>>>>                   goto restart;
>>>>           }
>>>> -       restarted = 0;
>>>>           done_iters = 0;
>>>>           gettimeofday(&tv_even, (struct timezone *)NULL);
>>>>
>>>> --
>>>> 2.51.0
>>>>
>>>>
>>>
>>>
>>
> 
>