linux-kernel - Re: [PATCH v1 1/6] perf header: Replace hardcoded max cpus by MAX_NR

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Message-ID: <4da60acc-cbce-4cd2-9600-8a151592d122@amd.com>
Date: Wed, 28 Jan 2026 23:59:29 +0530
From: Swapnil Sapkal <swapnil.sapkal@....com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
CC: Shrikanth Hegde <sshegde@...ux.ibm.com>, <mark.rutland@....com>,
	<alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
	<adrian.hunter@...el.com>, <thomas.falcon@...el.com>, <ashelat@...hat.com>,
	<yu.c.chen@...el.com>, <gautham.shenoy@....com>, <ravi.bangoria@....com>,
	<linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
	<peterz@...radead.org>, <mingo@...hat.com>, <namhyung@...nel.org>,
	<irogers@...gle.com>, <james.clark@....com>
Subject: Re: [PATCH v1 1/6] perf header: Replace hardcoded max cpus by
 MAX_NR_CPUS

Hello Arnaldo,

On 28-01-2026 23:45, Arnaldo Carvalho de Melo wrote:
> On Wed, Jan 28, 2026 at 09:55:05PM +0530, Swapnil Sapkal wrote:
>> Hi Srikanth, Arnaldo,
>>
>> Thank you for reviewing the patches.
>>
>> On 28-01-2026 13:09, Shrikanth Hegde wrote:
>>>
>>>
>>> On 1/28/26 12:19 AM, Swapnil Sapkal wrote:
>>>> cpumask and cpulist from cpu-domain header have hardcoded max_cpus value
>>>> of 1024. Current systems have more cpus than this value. Replace it with
>>>> MAX_NR_CPUS. Also define a macro to represent domain name length.
>>>>
>>>> Fixes: d40c68a49f69 ("perf header: Support CPU DOMAIN relation info")
>>>> Reported-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
>>>> Signed-off-by: Swapnil Sapkal <swapnil.sapkal@....com>
>>>> ---
>>>>    tools/perf/util/header.c | 5 +++--
>>>>    1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
>>>> index eefd1cd73b6a..31c3bab1b10a 100644
>>>> --- a/tools/perf/util/header.c
>>>> +++ b/tools/perf/util/header.c
>>>> @@ -76,6 +76,7 @@ static const u64 __perf_magic2    =
>>>> 0x32454c4946524550ULL;
>>>>    static const u64 __perf_magic2_sw = 0x50455246494c4532ULL;
>>>>    #define PERF_MAGIC    __perf_magic2
>>>> +#define DNAME_LEN    16
>>>>    const char perf_version_string[] = PERF_VERSION;
>>>> @@ -1616,10 +1617,10 @@ static int write_pmu_caps(struct feat_fd *ff,
>>>>    struct cpu_domain_map **build_cpu_domain_map(u32
>>>> *schedstat_version, u32 *max_sched_domains, u32 nr)
>>>>    {
>>>> +    char dname[DNAME_LEN], cpumask[MAX_NR_CPUS];
>>>>        struct domain_info *domain_info;
>>>>        struct cpu_domain_map **cd_map;
>>>> -    char dname[16], cpumask[256];
>>>> -    char cpulist[1024];
>>>> +    char cpulist[MAX_NR_CPUS];
>>>>        char *line = NULL;
>>>>        u32 cpu, domain;
>>>>        u32 dcount = 0;
>>>
>>> Looking at
>>> https://lore.kernel.org/all/20260119175833.340369-3-swapnil.sapkal@amd.com/
>>>
>>> There was one more "char cpus[1024]"  in tools/perf/util/util.c.
>>> You may need to fix that too. It is unlikely but, if one has created
>>> exclusive
>>> cpusets comprising of only one cpu from a core, maybe you will run out
>>> the length.
>>> So better use the MAX_NR_CPUS there as well.
>>
>> Yes, I missed this.
>>
>> Arnaldo, can you please consider the below diff? Let me know if you'd like
>> me to respin the patch.
>>
>> --
>> Thanks and Regards,
>> Swapnil
>>
>> diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
>> index c83e59e8c787..3795d5182ce8 100644
>> --- a/tools/perf/util/util.c
>> +++ b/tools/perf/util/util.c
>> @@ -262,7 +262,7 @@ void cpumask_to_cpulist(char *cpumask, char *cpulist)
>>          int i, j, bm_size, nbits;
>>          int len = strlen(cpumask);
>>          unsigned long *bm;
>> -       char cpus[1024];
>> +       char cpus[MAX_NR_CPUS];
>>
>>          for (i = 0; i < len; i++) {
>>                  if (cpumask[i] == ',') {
>> diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
>> index 394dbfa944ac..c43f17137efd 100644
>> --- a/tools/perf/util/util.h
>> +++ b/tools/perf/util/util.h
>> @@ -6,6 +6,7 @@
>>   /* glibc 2.20 deprecates _BSD_SOURCE in favour of _DEFAULT_SOURCE */
>>   #define _DEFAULT_SOURCE 1
>>
>> +#include "perf.h"
> 
> Why add it to util.h? I'll add it to where it is used, util.c, ok?
> 

This doesn't need to be in util.h. Please move it to util.c

--
Thanks and Regards,
Swapnil

> - Arnaldo
> 
>>   #include <dirent.h>
>>   #include <fcntl.h>
>>   #include <stdbool.h>