Re: aarch64 and kqueue timer events

From: Matthew Grooms <mgrooms_at_shrew.net>
Date: Tue, 27 Jul 2021 20:43:50 -0500
On 7/24/2021 8:18 PM, Matthew Grooms wrote:
> Hi all,
>
> I'm seeing some strange behavior with kqueue timers on my aarch64 
> host. Here is a simple test program that I've compiled on both amd64 
> and aarch64. It just sets up a simple kqueue timer with a loop that 
> waits for the event to fire every 3 seconds ...
>
> #include <err.h>
> #include <time.h>
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/event.h>
>
> int main( int argc, char *argv[] )
> {
>     int kq = kqueue();
>     if( kq < 0 )
>         err( 1, "failed to obtain kqueue handle" );
>
>     struct kevent ke;
>     EV_SET( &ke, 1, EVFILT_TIMER, EV_ADD | EV_ENABLE, 0, 3000, 0 );
>     if( kevent( kq, &ke, 1, NULL, 0, NULL ) < 0 )
>         err( 1, "failed to add kevent timer filter" );
>
>     printf( "started at %i\n", (int)time(NULL) );
>
>     while( true )
>     {
>         int r = kevent( kq, NULL, 0, &ke, 1, NULL );
>         if( r < 0 )
>             err( 1, "failed to read kevent list" );
>
>         printf( "timer fired %i times at %i\n", r, (int)time(NULL) );
>     }
>
>     return 0;
> }
>
> When I compile and run the code on an amd64 host, everything works as 
> expected. The event timer expires once every 3 seconds ...
>
> mgrooms_at_amd64:~/devel$ cc test.cpp -o test && ./test
> started at 1627175311
> timer fired 1 times at 1627175314
> timer fired 1 times at 1627175317
> timer fired 1 times at 1627175320
>
> However, when I compile and run the same code on an aarch64 host ( 
> rpi4b ), something very different happens. The event timer expires 
> after 3 seconds the first time. But each subsequent expiration is for 
> exactly twice the defined interval, 6 seconds ...
>
> mgrooms_at_aarch64:~/devel$ cc test.cpp -o test && ./test
> started at 1625789207
> timer fired 1 times at 1625789210
> timer fired 1 times at 1625789216
> timer fired 1 times at 1625789222
>
> Any idea what's going on here? Seems like a bug somewhere on the arm 
> side.
>
> Thanks in advance,
>
Hi Everyone,

Sorry for the cross post. I started by asking this question in 
freebsd-arm but didn't get a response. I figured, since aarch64 is Tier1 
now, asking wrt stable is fair game. Another user ( José Pérez ) 
confirmed that this issue was also present on current but my testing was 
on 13 ...

FreeBSD generic 13.0-STABLE FreeBSD 13.0-STABLE #8 
stable/13-n246015-ade8b810b02-dirty: Tue Jun 15 21:04:38 CDT 202

Any help would be greatly appreciated.

Thanks in advance,

-Matthew
Received on Wed Jul 28 2021 - 01:43:50 UTC

Original text of this message