Re: [9fans] Plan9 on Pi 3B+

[Skip Tavakkolian <skip.tavakkolian@gmail.com>]

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Thanks!   I got one recently and have been meaning to ask about his.

Running Linux, 3B+ seems perceptibly faster than 3B.

On Tue, Apr 3, 2018 at 2:05 PM, Richard Miller <9fans@hamnavoe.com> wrote:

> > But what is the
> > rationale for the lock in the second loop?
>
> Sorry for the confusing code.  The startlocks are locked by
> cpu0 before booting the secondary cores.  Each core unlocks
> its own startlock when it starts.  Cpu0 blocks on each startlock
> waiting for the corresponding core to unlock it, as a way of
> serialising the booting of the secondary cores (and detecting
> that they have started).
>
> If for some reason the secondary cpus don't start up, the
> result is a lock loop.  I really should have used canlock()
> instead, to expose a more helpful error message.  But it's
> a "should never happen" condition.
>
> It's happening with the new start_cd.elf because the Pi
> Foundation made a little change in the firmware which makes
> secondary cores wait with a WFE when booting, so the OS
> now has to do a SEV to wake them up.
>
> I'm just about to release an update to the bcm port for
> the 3B+, including drivers for the new "gigabit" ethernet
> (not really, because it's squeezed through a slow usb2 adapter)
> and the updated wifi chip.  But in the meantime the following
> should let you boot any pi2 or pi3 with the latest start_cd.elf:
>
> --- /sys/src/9/bcm/archbcm2.c   Fri Mar 16 17:08:21 2018
> ***************
> *** 167,172 ****
> --- 167,174 ----
>         if(mb->clr[cpu].startcpu)
>                 return -1;
>         mb->set[cpu].startcpu = PADDR(cpureset);
> +       coherence();
> +       sev();
>         for(i = 0; i < 1000; i++)
>                 if(mb->clr[cpu].startcpu == 0)
>                         return 0;
> ***************
> *** 196,202 ****
>   int
>   startcpus(uint ncpu)
>   {
> !       int i;
>
>         for(i = 0; i < ncpu; i++)
>                 lock(&startlock[i]);
> --- 198,204 ----
>   int
>   startcpus(uint ncpu)
>   {
> !       int i, timeout;
>
>         for(i = 0; i < ncpu; i++)
>                 lock(&startlock[i]);
> ***************
> *** 204,210 ****
>         for(i = 1; i < ncpu; i++){
>                 if(startcpu(i) < 0)
>                         return i;
> !               lock(&startlock[i]);
>                 unlock(&startlock[i]);
>         }
>         return ncpu;
> --- 206,215 ----
>         for(i = 1; i < ncpu; i++){
>                 if(startcpu(i) < 0)
>                         return i;
> !               timeout = 10000000;
> !               while(!canlock(&startlock[i]))
> !                       if(--timeout == 0)
> !                               return i;
>                 unlock(&startlock[i]);
>         }
>         return ncpu;
>
> --- /sys/src/9/bcm/armv7.s      Fri Mar 16 16:47:18 2018
> ***************
> *** 17,22 ****
> --- 17,23 ----
>   #define WFI   WORD    $0xe320f003     /* wait for interrupt */
>   #define WFI_EQ        WORD    $0x0320f003     /* wait for interrupt if
> eq */
>   #define ERET  WORD    $0xe160006e     /* exception return from HYP */
> + #define SEV   WORD    $0xe320f004     /* send event */
>
>   /* tas/cas strex debugging limits; started at 10000 */
>   #define MAXSC 1000000
> ***************
> *** 386,391 ****
> --- 387,396 ----
>
>   TEXT coherence(SB), $-4
>         BARRIERS
> +       RET
> +
> + TEXT sev(SB), $-4
> +       SEV
>         RET
>
>   /*
>
>
>

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