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improved drain_frontend

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This commit is contained in:
Andreas Abel
2022-01-12 20:33:09 +01:00
parent a1ad0fbf47
commit 39f97457c6
3 changed files with 20 additions and 8 deletions
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23
common/nanoBench.c
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@@ -453,7 +453,6 @@ size_t configure_perf_ctrs_programmable(size_t next_pfc_config, bool usr, bool o
continue;
}
if (((avoid_counters >> i) & 1) && (config.ctr != i)) {
print_error("avoiding %d", i);
continue;
}
next_pfc_config++;
@@ -491,7 +490,7 @@ size_t get_required_runtime_code_length() {
req_code_length += 100;
}
}
return code_init_length + code_late_init_length + (drain_frontend?3*64*15:0) + 2*unroll_count*req_code_length + 10000;
return code_init_length + code_late_init_length + (drain_frontend?3*(192+64*15):0) + 2*unroll_count*req_code_length + 10000;
}
int get_distance_to_code(char* measurement_template, size_t templateI) {
@@ -541,6 +540,9 @@ void create_runtime_code(char* measurement_template, long local_unroll_count, lo
if (drain_frontend) {
strcpy(&runtime_code[rcI], "\x0F\xAE\xE8"); rcI += 3; // lfence
for (int i=0; i<192; i++) {
strcpy(&runtime_code[rcI], NOPS[1]); rcI += 1;
}
for (int i=0; i<64; i++) {
strcpy(&runtime_code[rcI], NOPS[15]); rcI += 15;
}
@@ -562,19 +564,25 @@ void create_runtime_code(char* measurement_template, long local_unroll_count, lo
templateI += 8;
if (unrollI == 0 && codeI == 0) {
rcI_code_start = rcI;
if (code_late_init_length > 0) {
memcpy(&runtime_code[rcI], code_late_init, code_late_init_length);
rcI += code_late_init_length;
}
if (drain_frontend) {
// the length of the following code sequence is a multiple of 64, and thus doesn't affect the alignment
// We first execute an lfence instruction, then, we fill the front-end buffers with 1-Byte NOPs, and then, we drain the buffers using
// 15-Byte NOPs; this makes sure that before the first 15-Byte NOP is predecoded, the front-end buffers contain only NOPs that can be
// issued at the maximum rate. The length of the added instructions is a multiple of 64, and thus doesn't affect the alignment.
strcpy(&runtime_code[rcI], "\x0F\xAE\xE8"); rcI += 3; // lfence
for (int i=0; i<189; i++) {
strcpy(&runtime_code[rcI], NOPS[1]); rcI += 1;
}
for (int i=0; i<64; i++) {
strcpy(&runtime_code[rcI], NOPS[15]); rcI += 15;
}
}
rcI_code_start = rcI;
}
if (!code_contains_magic_bytes) {
@@ -611,8 +619,11 @@ void create_runtime_code(char* measurement_template, long local_unroll_count, lo
}
if (drain_frontend) {
// add an lfence and 64 nops s.t. the front end gets drained and the following instruction begins on a 32-byte boundary.
// We add an lfence followed by nop instructions s.t. the front end gets drained and the following instruction begins on a 32-byte boundary.
strcpy(&runtime_code[rcI], "\x0F\xAE\xE8"); rcI += 3; // lfence
for (int i=0; i<189; i++) {
strcpy(&runtime_code[rcI], NOPS[1]); rcI += 1;
}
for (int i=0; i<61; i++) {
strcpy(&runtime_code[rcI], NOPS[15]); rcI += 15;

3
common/nanoBench.h
View File

@@ -105,7 +105,8 @@ extern long initial_warm_up_count;
extern size_t alignment_offset;
#define ALIGNMENT_OFFSET_DEFAULT 0;
// If enabled, the front-end buffers are drained between code_late_init and code by executing a sequence of 128 15-Byte NOP instructions.
// If enabled, the front-end buffers are drained after code_init, after code_late_init, and after the last instance of code by executing an lfence, followed
// by a long sequence of 1-Byte NOPs, followed by a long sequence of 15-Byte NOPs.
extern int drain_frontend;
#define DRAIN_FRONTEND_DEFAULT false;