From: abush wang <abushwangs@gmail.com>
To: "H.J. Lu" <hjl.tools@gmail.com>,
abushwang via Libc-alpha <libc-alpha@sourceware.org>
Subject: x86-64: strlen-evex performance performance degradation compared to strlen-avx2
Date: Fri, 26 Apr 2024 12:03:20 +0800 [thread overview]
Message-ID: <CAMLoAPYs1FgpnTgJ36YxA2R71KAe+qfosRiqUMdrpHyKPCJ45w@mail.gmail.com> (raw)
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Hi, H.J.
When I test glibc performance between 2.28 and 2.38,
I found there is a performance degradation about strlen.
In fact, this difference comes from __strlen_avx2 and __strlen_evex
```
2.28
__strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:42
42 ENTRY (STRLEN)
2.38
__strlen_evex () at ../sysdeps/x86_64/multiarch/strlen-evex.S:79
79 ENTRY_P2ALIGN (STRLEN, 6)
```
This is my test:
```
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#define MAX_STRINGS 100
uint64_t rdtsc() {
uint32_t lo, hi;
__asm__ __volatile__ (
"rdtsc" : "=a"(lo), "=d"(hi)
);
return ((uint64_t)hi << 32) | lo;
}
int main(int argc, char *argv[]) {
char *input_str[MAX_STRINGS];
size_t lengths[MAX_STRINGS];
int num_strings = 0; // Number of input strings
uint64_t start_cycles, end_cycles;
// Parse command line arguments and store pointers in input_str array
for (int i = 1; i < argc && num_strings < MAX_STRINGS; ++i) {
input_str[num_strings] = argv[i];
num_strings++;
}
// Measure the strlen operation for each string
start_cycles = rdtsc();
for (int i = 0; i < num_strings; ++i) {
lengths[i] = strlen(input_str[i]);
}
end_cycles = rdtsc();
unsigned long long total_cycle = end_cycles - start_cycles;
unsigned long long av_cycle = total_cycle / num_strings;
// Print the total cycles taken for the strlen operations
printf("Total cycles: %llu av cycle: %llu \n", total_cycle, av_cycle);
// Print the recorded lengths
printf("Lengths of the input strings:\n");
for (int i = 0; i < num_strings; ++i) {
printf("String %d length: %zu\n", i, lengths[i]);
}
return 0;
}
```
This is result
```
2.28
./strlen_test str1 str2 str3 str4 str5
Total cycles: 1468 av cycle: 293
Lengths of the input strings:
String 0 length: 4
String 1 length: 4
String 2 length: 4
String 3 length: 4
String 4 length: 4
2.38
./strlen_test str1 str2 str3 str4 str5
Total cycles: 1814 av cycle: 362
Lengths of the input strings:
String 0 length: 4
String 1 length: 4
String 2 length: 4
String 3 length: 4
String 4 length: 4
```
Thanks,
abush
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next reply other threads:[~2024-04-26 4:04 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 4:03 abush wang [this message]
2024-04-26 13:30 ` x86-64: strlen-evex performance performance degradation compared to strlen-avx2 H.J. Lu
2024-04-26 16:53 ` Sunil Pandey
2024-04-28 2:13 ` abush wang
2024-04-28 16:12 ` Sunil Pandey
2024-04-28 16:16 ` H.J. Lu
2024-04-29 17:41 ` Sunil Pandey
2024-04-29 20:19 ` H.J. Lu
2024-04-30 0:54 ` Sunil Pandey
2024-04-30 2:51 ` H.J. Lu
2024-04-30 20:16 ` Sunil Pandey
2024-04-28 2:06 ` abush wang
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