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

[Alex Hung]

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 <visitor...@gmail.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.

  #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]);