net/http: unexpectedly slow initialization

Here is trivial program that makes GET request:

import (
        "fmt"
        "io/ioutil"
        "log"
        "net/http"
)

func main() {
        resp, _ := http.Get("https://ifconfig.me")
        defer resp.Body.Close()
        body, err := ioutil.ReadAll(resp.Body)
        if err != nil {
                log.Fatal(err)
        }

        fmt.Print(string(body))
}

When compiled and run on Darwin system (using binary distribution), it have more or less expected performance -- twice as slow compared to curl.

$ /usr/bin/time ./hello
173.66.169.194        0.25 real         0.05 user         0.01 sys
$ /usr/bin/time curl https://ifconfig.me
173.66.169.194        0.12 real         0.01 user         0.01 sys

But when I compile and run it on my Linux box (Linux void-live 5.13.13_1 #1 SMP Fri Aug 27 13:28:13 UTC 2021 x86_64 GNU/Linux), also using binary distribution, I get following results:

$ time ./hello
173.66.169.194
real      0m 1.03s
user    0m 1.30s
sys     0m 0.14s
$ time curl https://ifconfig.me
173.66.169.194
real      0m 0.16s
user    0m 0.06s
sys     0m 0.00s

Difference is much bigger. This time seems to come from some one-time initialization -- second request made in same program is fast. Here is annotated strace. It looks like it is doing many "rt_sigreturn" calls, but this is just my guess.

I have access to another linux box, with unusual kernel (lacking madvise(2), for example), which have more of the same problem: first request takes around 4 seconds, any subsequent work as expected.