Re: AGP and PAT (induced?) problem (on AMD family 6)

[Ingo Molnar <mingo@elte.hu>]

(more people Cc:-ed)

* Rene Herman <rene.herman@keyaccess.nl> wrote:

> Hi Dave.
>
> A while ago I sent a message about long AGP delays upon starting and 
> exiting X:
>
> http://marc.info/?l=linux-kernel&m=121647129632110&w=2
>
> There was no reply (if that was due to the linux.ie address, could you  
> perhaps update it in MAINTAINERS?) but today Shaohua Li posted a patch  
> that made me wonder about PAT in this context:
>
> http://marc.info/?l=linux-kernel&m=121783222306075&w=2
> http://marc.info/?l=linux-kernel&m=121783222406078&w=2
> http://marc.info/?l=linux-kernel&m=121783222406081&w=2
>
> His patch does not solve anything appreciable for me -- the delays are  
> still as described in that previous post, with an exception for (with  
> Option "AGSize" "64") delays upon exiting X that are now sometimes as  
> bad as a full 12 seconds.
>
> What _does_ solve this though is booting with the "nopat" command line  
> parameter. I'm on 2.6.26.1 and have enabled PAT for my AMD Duron myself.  
> With "nopat", there's no problem to be seen anymore -- exiting X  
> specifically is instantaneous.
>
> With or without PAT, my /proc/mtrr is always:
>
> reg00: base=0x00000000 (   0MB), size= 512MB: write-back, count=1
> reg01: base=0x20000000 ( 512MB), size= 256MB: write-back, count=1
> reg02: base=0xe8000000 (3712MB), size=  64MB: write-combining, count=1
>
> under X joined by:
>
> reg03: base=0xe4000000 (3648MB), size=  32MB: write-combining, count=2
>
> This is a machine with 768M, the AGP aperture set to 64MB and a 32MB  
> Matrox Millenium G550 AGP card. More detail in previous post.
>
> Is this something inherent to PAT? Inherent to PAT on AMD family 6?  
> Inherent to DRM/AGP with PAT? On AMD family 6?
>
> This is probably fairly important to get sorted because although I don't  
> know what's where at the moment, last I saw was a patch in x86/tip that  
> enabled PAT on many more models including all of AMD.
>
> For reference, /proc/cpuinfo:
>
> processor	: 0
> vendor_id	: AuthenticAMD
> cpu family	: 6
> model		: 7
> model name	: AMD Duron(tm) Processor
> stepping	: 1
> cpu MHz		: 1313.094
> cache size	: 64 KB
> fdiv_bug	: no
> hlt_bug		: no
> f00f_bug	: no
> coma_bug	: no
> fpu		: yes
> fpu_exception	: yes
> cpuid level	: 1
> wp		: yes
> flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov  
> pat pse36 mmx fxsr sse syscall mmxext 3dnowext 3dnow
> bogomips	: 2628.89
> clflush size	: 32
> power management: ts
>
> and the PAT enabler patch that I apply locally to 2.6.26:
>
> diff --git a/arch/x86/kernel/cpu/addon_cpuid_features.c  
> b/arch/x86/kernel/cpu/addon_cpuid_features.c
> index c2e1ce3..8992282 100644
> --- a/arch/x86/kernel/cpu/addon_cpuid_features.c
> +++ b/arch/x86/kernel/cpu/addon_cpuid_features.c
> @@ -55,7 +55,7 @@ void __cpuinit validate_pat_support(struct cpuinfo_x86 *c)
>  {
>         switch (c->x86_vendor) {
>         case X86_VENDOR_AMD:
> -               if (c->x86 >= 0xf && c->x86 <= 0x11)
> +               if (c->x86 == 6 || c->x86 >= 0xf)
>                         return;
>                 break;
>         case X86_VENDOR_INTEL:

agreed - +12 seconds wait suggest some rather fundamental breakage. Did 
we go back to uncached for some critical display area that makes X start 
up (shut down) that slowly? Did we mark the BIOS uncacheable perhaps, 
causing X to execute BIOS code very slowly?

	Ingo