kern/57273: poll timeout is doubled when NetBSD is run inside QEMU

[roy%marples.name@localhost]

>Number:         57273
>Category:       kern
>Synopsis:       poll timeout is doubled when NetBSD is run inside QEMU
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Mar 16 16:55:00 +0000 2023
>Originator:     Roy Marples
>Release:        NetBSD-9.3
>Organization:
>Environment:
NetBSD netbsd9 9.3_STABLE NetBSD 9.3_STABLE (GENERIC) #0: Mon Mar 13 21:38:46 UTC 2023  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
>Description:
Testing dhcpcd timings in a NetBSD vm is impossible because the time to sleep with any polling mechanism (poll, pollts, kqueue) is doubled.
Outside the vm, on bare metal, it works fine.
>How-To-Repeat:
Install NetBSD to a qemu VM hosted on NetBSD.

Reproducer:

#include <poll.h>
#include <stdio.h>
#include <time.h>

int
main(void)
{
        struct timespec ts = { .tv_sec = 10 };
        struct timespec start, end;

        fprintf(stderr, "ppoll timeout %ld secs\n", ts.tv_sec);
        clock_gettime(CLOCK_MONOTONIC, &start);
        fprintf(stderr, "poll start is %ld, timeout is %ld, end should be %ld\n",
            start.tv_sec, ts.tv_sec, start.tv_sec + ts.tv_sec);
        pollts(NULL, 0, &ts, NULL);
        clock_gettime(CLOCK_MONOTONIC, &end);
        fprintf(stderr, "poll end is %ld, off by %ld secs\n",
            end.tv_sec, end.tv_sec - (start.tv_sec + ts.tv_sec));
        return 0;
}
>Fix: