powerpc/perf: Optimize find_alternatives_list() using binary search

This patch improves the performance of event alternative lookup by
replacing the previous linear search with a more efficient binary
search. This change reduces the time complexity for the search process
from O(n) to O(log(n)). A pre-sorted table of event values and their
corresponding indices has been introduced to expedite the search
process.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
[mpe: Call the array "presort*ed*_event_table", minor formatting]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231013175714.2142775-1-visitorckw@gmail.com

diff --git a/arch/powerpc/perf/power6-pmu.c b/arch/powerpc/perf/power6-pmu.c
index 5729b6e059de05caecc5da69cca09072280ca992..9f720b522e17143bdf28ecd4712f046f36fbd008 100644 (file)
--- a/arch/powerpc/perf/power6-pmu.c
+++ b/arch/powerpc/perf/power6-pmu.c
@@ -335,26 +335,38 @@ static const unsigned int event_alternatives[][MAX_ALT] = {
        { 0x3000fe, 0x400056 },                 /* PM_DATA_FROM_L3MISS */
 };
 
-/*
- * This could be made more efficient with a binary search on
- * a presorted list, if necessary
- */
 static int find_alternatives_list(u64 event)
 {
-       int i, j;
-       unsigned int alt;
-
-       for (i = 0; i < ARRAY_SIZE(event_alternatives); ++i) {
-               if (event < event_alternatives[i][0])
-                       return -1;
-               for (j = 0; j < MAX_ALT; ++j) {
-                       alt = event_alternatives[i][j];
-                       if (!alt || event < alt)
-                               break;
-                       if (event == alt)
-                               return i;
-               }
+       const unsigned int presorted_event_table[] = {
+               0x0130e8, 0x080080, 0x080088, 0x10000a, 0x10000b, 0x10000d, 0x10000e,
+               0x100010, 0x10001a, 0x100026, 0x100054, 0x100056, 0x1000f0, 0x1000f8,
+               0x1000fc, 0x200008, 0x20000e, 0x200010, 0x200012, 0x200054, 0x2000f0,
+               0x2000f2, 0x2000f4, 0x2000f5, 0x2000f6, 0x2000f8, 0x2000fc, 0x2000fe,
+               0x2d0030, 0x30000a, 0x30000c, 0x300010, 0x300012, 0x30001a, 0x300056,
+               0x3000f0, 0x3000f2, 0x3000f6, 0x3000f8, 0x3000fc, 0x3000fe, 0x400006,
+               0x400007, 0x40000a, 0x40000e, 0x400010, 0x400018, 0x400056, 0x4000f0,
+               0x4000f8, 0x600005
+       };
+       const unsigned int event_index_table[] = {
+               0,  1,  2,  3,  4,  1, 5,  6,  7,  8,  9,  10, 11, 12, 13, 12, 14,
+               7,  15, 2,  9,  16, 3, 4,  0,  17, 10, 18, 19, 20, 1,  17, 15, 19,
+               18, 2,  16, 21, 8,  0, 22, 13, 14, 11, 21, 5,  20, 22, 1,  6,  3
+       };
+       int hi = ARRAY_SIZE(presorted_event_table) - 1;
+       int lo = 0;
+
+       while (lo <= hi) {
+               int mid = lo + (hi - lo) / 2;
+               unsigned int alt = presorted_event_table[mid];
+
+               if (alt < event)
+                       lo = mid + 1;
+               else if (alt > event)
+                       hi = mid - 1;
+               else
+                       return event_index_table[mid];
        }
+
        return -1;
 }