Commit e08c43e6 authored by Kuan-Wei Chiu's avatar Kuan-Wei Chiu Committed by Michael Ellerman
Browse files

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: default avatarKuan-Wei Chiu <visitorckw@gmail.com>
[mpe: Call the array "presort*ed*_event_table", minor formatting]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231013175714.2142775-1-visitorckw@gmail.com
parent d45c4b48

arch/powerpc/perf/power6-pmu.c

+29 −17
Original line number Diff line number Diff line
@@ -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;

}