RFC: Hiding per-CPU kernel output behind bootverbose

[Colin Percival]

On 04/21/18 12:52, Warner Losh wrote:
>     On Sat, 21 Apr 2018 12:20:49 +0300
>     Konstantin Belousov <kib at freebsd.org <mailto:kib at freebsd.org>> wrote:
>     > On Sat, Apr 21, 2018 at 12:11:07AM +0000, Colin Percival wrote:
>     > > Would it be sufficient for debugging purposes if I change the !bootverbose
>     > > case from printing many lines of
>     > >
>     > > SMP: AP CPU #N Launched!
>     > >
>     > > to instead have a single
>     > >
>     > > SMP: Launching AP CPUs: 86 73 111 21 8 77 100 28 57 42 10 60 87 [...]
>     > >
>     > > ?  (With each AP printing its number as it reaches the appropriate point?)
>     > I am fine with the behaviour, but I am not sure how would you implement
>     > this.  printf(9) buffers the output, you need to flush it somehow.
> 
> I don't think either of these is true (the double buffered part,. nor the
> buffered part). Well, they are both kinda true, but they don't matter. It's
> all to make dmesg and friends work. There's other issues, but at this stage of
> the boot we're single threaded and the CPUs that are launching take out a spin
> lock.

I just checked (by adding a 500 ms delay after each CPU prints its ID) and I
can definitely see the individual numbers being printed on the console.

> diff --git a/sys/x86/x86/mp_x86.c b/sys/x86/x86/mp_x86.c
> index 3fcf7aa25152..06973b1ea6d5 100644
> --- a/sys/x86/x86/mp_x86.c
> +++ b/sys/x86/x86/mp_x86.c
> @@ -1020,7 +1020,7 @@ init_secondary_tail(void)
>         smp_cpus++;
> 
>         CTR1(KTR_SMP, "SMP: AP CPU #%d Launched", cpuid);
> -       printf("SMP: AP CPU #%d Launched!\n", cpuid);
> +       printf("%d%s", cpuid, smp_cpus == mp_ncpus ? "\n" : " ");
> 
>         /* Determine if we are a logical CPU. */
>         if (cpu_info[PCPU_GET(apic_id)].cpu_hyperthread)
> 
> is enough to give them all to me on a single line. We'd need another printf
> that says 'Starting APs: ' since otherwise we see:
> 
> andom: unblocking device.
> ioapic0 <Version 2.0> irqs 0-23 on motherboard
> ioapic1 <Version 2.0> irqs 24-47 on motherboard
> 1 8 10 20 2 19 11 12 22 4 14 23 16 13 3 18 5 17 21 9 15 6 7
> Timecounter "TSC-low" frequency 1350029824 Hz quality 1000
> 
> which doesn't make a lot of sense.
> 
> Comments?

Here's the patch I have, which prints a header before the CPU IDs:

Index: sys/x86/x86/mp_x86.c
===================================================================
--- sys/x86/x86/mp_x86.c        (revision 332638)
+++ sys/x86/x86/mp_x86.c        (working copy)
@@ -1020,7 +1020,9 @@
        smp_cpus++;

        CTR1(KTR_SMP, "SMP: AP CPU #%d Launched", cpuid);
-       printf("SMP: AP CPU #%d Launched!\n", cpuid);
+       printf(" %d", cpuid);
+       if (smp_cpus == mp_ncpus)
+               printf("\n");

        /* Determine if we are a logical CPU. */
        if (cpu_info[PCPU_GET(apic_id)].cpu_hyperthread)
@@ -1508,6 +1510,7 @@

        if (mp_ncpus == 1)
                return;
+       printf("SMP: Launching AP CPUs:");
        atomic_store_rel_int(&aps_ready, 1);
        while (smp_started == 0)
                ia32_pause();

-- 
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid