41 lines · c
1#include <linux/compiler.h>2#include "../tests.h"3 4typedef struct _buf {5 char data1;6 char reserved[55];7 char data2;8} buf __attribute__((aligned(64)));9 10static buf buf1 = {11 /* to have this in the data section */12 .reserved[0] = 1,13};14 15static int datasym(int argc __maybe_unused, const char **argv __maybe_unused)16{17 for (;;) {18 buf1.data1++;19 if (buf1.data1 == 123) {20 /*21 * Add some 'noise' in the loop to work around errata22 * 1694299 on Arm N1.23 *24 * Bias exists in SPE sampling which can cause the load25 * and store instructions to be skipped entirely. This26 * comes and goes randomly depending on the offset the27 * linker places the datasym loop at in the Perf binary.28 * With an extra branch in the middle of the loop that29 * isn't always taken, the instruction stream is no30 * longer a continuous repeating pattern that interacts31 * badly with the bias.32 */33 buf1.data1++;34 }35 buf1.data2 += buf1.data1;36 }37 return 0;38}39 40DEFINE_WORKLOAD(datasym);41