Re: [PATCH] stdlib: reorganize stdlib Makefile routines by functionality

[abush wang <abushwangs@gmail.com>]

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Actually, not just d275970ab
I found after a91bf4e0ff, there is also performance degradation on x86-64,
even if this commit has nothing  to do with lrand48.
This is my test data:
before  a91bf4e0ff:
Average time for lrand48: 1940 cycles

after:
Average time for lrand48: 5626 cycles

It seems like there is a gradual performance degradation for lrand48.


On Tue, Apr 2, 2024 at 10:17 AM abush wang <abushwangs@gmail.com> wrote:

> Yes，on x86-64.
> I just compare the disassemble between d275970ab and before commit by
> objdump.
> And __drand48_iterate will be more long distance after d275970ab, so I
> revert this
> commit and found the performance will recover a little.
>
> Thanks,
> abush
>
>
> On Mon, Apr 1, 2024 at 9:12 PM Florian Weimer <fweimer@redhat.com> wrote:
>
>> * abush wang:
>>
>> > This is test:
>> > ```
>> > uint64_t getnsecs() {
>> >     uint32_t lo, hi;
>> >     __asm__ __volatile__ (
>> >         "rdtsc" : "=a"(lo), "=d"(hi)
>> >     );
>> >     return ((uint64_t)hi << 32) | lo;
>> > }
>> >
>> > int main() {
>> >     const int num_iterations = 1;
>> >     uint64_t start, end, total_time = 0;
>> >
>> >     start = getnsecs();
>> >     for (int i = 0; i < num_iterations; i++) {
>> >         (void) lrand48();
>> >     }
>> >     end = getnsecs();
>> >     total_time += (end - start);
>> >
>> >     printf("Average time for lrand48: %lu cycles\n", total_time /
>> num_iterations);
>> >     return 0;
>> > }
>> > ```
>> > before:
>> > Average time for lrand48: 21418 cycles
>> >
>> > after:
>> > Average time for lrand48: 9892 cycles
>>
>> Do you see this on x86-64?  So this isn't a displacement range issue?
>>
>> It could be that this is a random performance change due to code
>> alignment, and not actually caused by the direct call distance.
>>
>> Thanks,
>> Florian
>>
>>