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powerpc/perf: Optimize find_alternatives_list() using binary search

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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
This commit is contained in:
Kuan-Wei Chiu 2023-10-14 01:57:14 +08:00 committed by Michael Ellerman
parent d45c4b48da
commit e08c43e6c3
1 changed files with 28 additions and 16 deletions
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44
arch/powerpc/perf/power6-pmu.c
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@ -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;
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;
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;
}
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;
}