linux-kernel - Re: [PATCH 5/7] selftests/resctrl: Use pointers to build benchmark cmd and make it const

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Date:   Wed, 16 Aug 2023 14:52:22 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC:     Shuah Khan <skhan@...uxfoundation.org>,
        <linux-kselftest@...r.kernel.org>, Shuah Khan <shuah@...nel.org>,
        Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH 5/7] selftests/resctrl: Use pointers to build benchmark
 cmd and make it const

Hi Ilpo,

On 8/16/2023 12:13 AM, Ilpo Järvinen wrote:
> On Tue, 15 Aug 2023, Reinette Chatre wrote:
>> On 8/15/2023 2:42 AM, Ilpo Järvinen wrote:
>>> On Mon, 14 Aug 2023, Reinette Chatre wrote:
>>>>
>>>> On 8/8/2023 2:16 AM, Ilpo Järvinen wrote:

...
>>>>> diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
>>>>> index bcd0d2060f81..ddb1e83a3a64 100644
>>>>> --- a/tools/testing/selftests/resctrl/resctrl.h
>>>>> +++ b/tools/testing/selftests/resctrl/resctrl.h
>>>>> @@ -6,6 +6,7 @@
>>>>>  #include <math.h>
>>>>>  #include <errno.h>
>>>>>  #include <sched.h>
>>>>> +#include <stdint.h>
>>>>>  #include <stdlib.h>
>>>>>  #include <unistd.h>
>>>>>  #include <string.h>
>>>>> @@ -38,7 +39,14 @@
>>>>>  
>>>>>  #define END_OF_TESTS	1
>>>>>  
>>>>> +#define BENCHMARK_ARGS		64
>>>>> +
>>>>> +/* Approximate %zu max length */
>>>>> +#define SIZE_MAX_DECIMAL_SIZE	(sizeof(SIZE_MAX) * 8 / 3 + 2)
>>>>> +
>>>>> +/* Define default span both as integer and string, these should match */
>>>>>  #define DEFAULT_SPAN		(250 * MB)
>>>>> +#define DEFAULT_SPAN_STR	"262144000"
>>>>
>>>> I think above hardcoding can be eliminated by using asprintf()? This
>>>> does allocate memory though so I would like to understand why one
>>>> goal is to not dynamically allocate memory.
>>>
>>> Because it's simpler on the _free() side_. If there's no allocation, no 
>>> free() is needed.
>>>
>>> Only challenge that remains is the int -> string conversion for the 
>>> default span which can be either done like in the patch or using some 
>>> preprocessor trickery to convert the number to string. If you prefer the 
>>> latter, I can change to that so it's not hardcoded both as int and string.
>>>
>>
>> This manual int->string sounds like the trickery to me and can be avoided
>> by just using asprintf(). I understand that no free() is needed when no
>> memory is allocated but it looks to me as though these allocations can
>> be symmetrical - allocate the memory before the tests are run and free it
>> after?
> 
> It could be symmetrical but that means I'll be doing unnecessary alloc if 
> -b is provided which I assume you're against given your comment on always 
> creating copy of cmd in CMT test's case.

I seemed to have lost track here ... could you please elaborate where the
unnecessary alloc will be?

> 
> I think I'll use similar resolution to this as CMT test does, it has an 
> extra variable which is NULL in when -b is provided so free() is no-op
> on that path. Then I can use asprintf().
> 

Reinette