Re: 2.1.93 uniprocessor with SMP kernel -- partial success

Linus Torvalds (torvalds@transmeta.com)
Wed, 8 Apr 1998 11:37:28 -0700 (PDT)

On Wed, 8 Apr 1998, Adam J. Richter wrote:
>
> The following patch apparently enables a 2.1.93 kernel
> compiled with SMP to run on a uniprocessor system. However, this
> patch is probably not the whole story, because:
>
> 1. After booting 2.1.93, I started composing this letter
> and editting a file under X windows ( + Xemacs and a couple of
> xterm's), and, in the midst of that, my machine locked up hard.
>
> 2. printk's seem very slow. There seems to be a pause
> every time a new line is printed. The result is somelike
> like a 2400 baud console, although the pauses are between
> lines rather than between characters.

The 2.1.93 kernel has a major bug, which is that CONFIG_SERIAL_ECHO is
forced on by default in console.c. That makes printk's very slow, and I
wonder what other effects it could have on machines that don't have
anything attached to the default port (or even worse, _have_ something
attached and want to use it).

> ----------------------CUT HERE-----------------------------------------
> --- /tmp/linux/arch/i386/mm/init.c Wed Apr 8 10:42:02 1998
> +++ linux/arch/i386/mm/init.c Wed Apr 8 10:42:45 1998
> @@ -293,12 +293,13 @@
> }
>
> local_flush_tlb();
> +#if 0 /* These printk's reboot uniprocessor systems. -adam@yggdrasil.com */
> printk("IO APIC ID: %d\n", *(int *)0xFEC00000);
> printk("APIC ID: %d\n", *(int *)0xFEE00000);
> +#endif /* 0 */

Thanks, done.

Linus

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