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

(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


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