Potential performance regression of vformat_to in libfmt 11 compared to libfmt 10.2.1 #4070
Description
Hello,
I am experiencing a drop in throughput when migrating my logging library to libfmt 11 compared to libfmt 10.2.1.
I haven't been able to figure out yet if this is something related to my project or the newer version of libfmt, but the only change is the libfmt library.
Environment
Compiler: GCC 13
OS: Linux RHEL
Build Configuration: Release build with -O3 -DNDEBUG -std=gnu++20
libfmt: Header-only version
#include "quill/bundled/fmt/base.h"
#include "quill/bundled/fmt/format.h"
#include <string>
#include <iostream>
#include <chrono>
#include <atomic>
void ClobberMemory() {
std::atomic_signal_fence(std::memory_order_acq_rel);
}
int main()
{
using format_buffer_t = fmt::basic_memory_buffer<char>;
fmt::string_view format_str = "Hello, {}. The answer is {} and {}.";
int a = 1;
int b = 2345;
int c = 6789;
auto args = fmt::make_format_args(a, b, c);
const int n = 10'000'000;
auto start = std::chrono::high_resolution_clock::now();
for (int iteration = 0; iteration < n; ++iteration)
{
format_buffer_t buffer;
fmt::vformat_to(std::back_inserter(buffer), format_str, args);
}
ClobberMemory();
auto end = std::chrono::high_resolution_clock::now();
std::chrono::duration<double> duration = end - start;
double total_time = duration.count() * 1000; // Convert to milliseconds
std::cout << "Total time for formatting " << n << " strings: "
<< total_time << " ms" << std::endl;
return 0;
}I ran the above several times for both versions and it seems that version 10.2.1 is always faster. I am running it on an isolated cpu and nothing else is running on the whole box
Are there any known changes in libfmt 11 that could explain this difference?