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

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Date:   Thu, 17 Aug 2023 11:32:28 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Reinette Chatre <reinette.chatre@...el.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

On Wed, 16 Aug 2023, Reinette Chatre wrote:
> 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?

If there's what you call "symmetry", it implies the code always does 
alloc. However, the logic in main() is such that when -b is provided, no 
default benchmark command needs to be assigned, so no alloc for span is 
necessary. Thus, there either is unnecessary alloc with -b or _no 
symmetry_.

But I've already converted to asprintf() so no need to continue this 
discussion.

> > 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
> 

-- 
 i.