linux-kernel - Re: [PATCH 1/2] drm/amd/display: Optimize reserved time candidates sorting using standard sort()

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Message-ID: <655a009a-0b69-4e11-949e-ff0f47b424d5@amd.com>
Date: Mon, 8 Sep 2025 19:35:08 +0200
From: Christian König <christian.koenig@....com>
To: Alex Hung <alex.hung@....com>, Kuan-Wei Chiu <visitorckw@...il.com>,
 austin.zheng@....com, jun.lei@....com, harry.wentland@....com,
 sunpeng.li@....com, siqueira@...lia.com, alexander.deucher@....com,
 airlied@...il.com, simona@...ll.ch
Cc: zaeem.mohamed@....com, wenjing.liu@....com, chiahsuan.chung@....com,
 Natanel.Roizenman@....com, Daniel.Sa@....com, jserv@...s.ncku.edu.tw,
 amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drm/amd/display: Optimize reserved time candidates
 sorting using standard sort()

On 08.09.25 19:05, Alex Hung wrote:
> 
> 
> On 8/24/25 12:23, Kuan-Wei Chiu wrote:
>> Replace the custom bubble sort used for sorting reserved time
>> candidates in with the kernel's standard sort() helper. The previous
>> code had O(N^2) time complexity, while the generic kernel sort runs in
>> O(N log N). This improves efficiency and removes the need for a local
>> sorting implementation, while keeping functionality unchanged.
>>
>> Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
>> ---
>> Compile test only.
>>
>>   .../dml2/dml21/src/dml2_pmo/dml2_pmo_dcn3.c   | 23 +++++++++++--------
>>   1 file changed, 13 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn3.c b/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn3.c
>> index e763c8e45da8..2b13a5e88917 100644
>> --- a/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn3.c
>> +++ b/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn3.c
>> @@ -2,19 +2,21 @@
>>   //
>>   // Copyright 2024 Advanced Micro Devices, Inc.
>>   +#include <linux/sort.h>
>> +
> 
> Thanks for working on this, but this file is shared with another OS and it is not possible to replace sort function with Linux-only sort.

That's not a valid argument. Linux code must be solely written for Linux, you can't reject a valid patch because it breaks sharing code with other operating systems.

Regards,
Christian.

> 
>>   #include "dml2_pmo_factory.h"
>>   #include "dml2_pmo_dcn3.h"
>>   -static void sort(double *list_a, int list_a_size)
>> +static int cmp_double(const void *a, const void *b)
>>   {
>> -    // For all elements b[i] in list_b[]
>> -    for (int i = 0; i < list_a_size - 1; i++) {
>> -        // Find the first element of list_a that's larger than b[i]
>> -        for (int j = i; j < list_a_size - 1; j++) {
>> -            if (list_a[j] > list_a[j + 1])
>> -                swap(list_a[j], list_a[j + 1]);
>> -        }
>> -    }
>> +    double da = *(const double *)a;
>> +    double db = *(const double *)b;
>> +
>> +    if (da < db)
>> +        return -1;
>> +    if (da > db)
>> +        return 1;
>> +    return 0;
>>   }
>>     static double get_max_reserved_time_on_all_planes_with_stream_index(struct display_configuation_with_meta *config, unsigned int stream_index)
>> @@ -634,7 +636,8 @@ bool pmo_dcn3_init_for_pstate_support(struct dml2_pmo_init_for_pstate_support_in
>>             // Finally sort the array of candidates
>>           sort(pmo->scratch.pmo_dcn3.reserved_time_candidates[stream_index],
>> -            pmo->scratch.pmo_dcn3.reserved_time_candidates_count[stream_index]);
>> +             pmo->scratch.pmo_dcn3.reserved_time_candidates_count[stream_index],
>> +             sizeof(double), cmp_double, NULL);
>>             remove_duplicates(pmo->scratch.pmo_dcn3.reserved_time_candidates[stream_index],
>>               &pmo->scratch.pmo_dcn3.reserved_time_candidates_count[stream_index]);
>