linux-kernel - Re: [PATCH v4] sched/topology: Enable topology_span

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Message-ID: <d033e4cc-728e-41cd-8fd8-616b2eb7709f@amd.com>
Date: Fri, 7 Mar 2025 21:11:46 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Naman Jain <namjain@...ux.microsoft.com>, Valentin Schneider
	<vschneid@...hat.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra
	<peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
	<vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
 Gorman <mgorman@...e.de>
CC: <stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Steve Wahl
	<steve.wahl@....com>, Saurabh Singh Sengar <ssengar@...ux.microsoft.com>,
	<srivatsa@...il.mit.edu>, Michael Kelley <mhklinux@...look.com>, Shrikanth
 Hegde <sshegde@...ux.ibm.com>
Subject: Re: [PATCH v4] sched/topology: Enable topology_span_sane check only
 for debug builds

Hello Naman,

On 3/7/2025 8:35 PM, Naman Jain wrote:
> 
> 
> On 3/6/2025 10:18 PM, Valentin Schneider wrote:
>> On 06/03/25 11:23, Naman Jain wrote:
>>> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
>>> index c49aea8c1025..666f0a18cc6c 100644
>>> --- a/kernel/sched/topology.c
>>> +++ b/kernel/sched/topology.c
>>> @@ -2359,6 +2359,13 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl,
>>>   {
>>>        int i = cpu + 1;
>>>
>>> +    /* Skip the topology sanity check for non-debug, as it is a time-consuming operation */
>>> +    if (!sched_debug()) {
>>> +        pr_info_once("%s: Skipping topology span sanity check. Use `sched_verbose` boot parameter to enable it.\n",
>>> +                 __func__);
>>
>> FWIW I'm not against this change, however if you want to add messaging
>> about sched_verbose I'd put that in e.g. sched_domain_debug() (as a print
>> once like you've done here) with something along the lines of:
>>
>>    "Scheduler topology debugging disabled, add 'sched_verbose' to the cmdline to enable it"
> 
> 
> Thank you so much for reviewing.
> Please correct me if I misunderstood. Are you proposing below change?
> 
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -2361,7 +2361,7 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl,
> 
>          /* Skip the topology sanity check for non-debug, as it is a time-consuming operation */
>          if (!sched_debug()) {
> -               pr_info_once("%s: Skipping topology span sanity check. Use `sched_verbose` boot parameter to enable it.\n",
> +               pr_info_once("%s: Scheduler topology debugging disabled, add 'sched_verbose' to the cmdline to enable it\n",
>                               __func__);
>                  return true;
>          }
> 

I think Valentin meant moving the same pr_info_once() to the early exit
case in sched_domain_debug() for "!sched_debug_verbose" to notify the
user that sched_debug() is disabled and they can turn it on using
"sched_verbose" as opposed to announcing it from topology_span_sane().

-- 
Thanks and Regards,
Prateek

> 
> Regards,
> Naman
> 
>>
>>> +        return true;
>>> +    }
>>> +
>>>        /* NUMA levels are allowed to overlap */
>>>        if (tl->flags & SDTL_OVERLAP)
>>>                return true;
>>> -- 
>>> 2.34.1
>