On Thursday, June 21, 2007 12:40:58 Yinghai Lu wrote:
> On 6/7/07, Jesse Barnes <[email protected]> wrote:
> > On some machines, buggy BIOSes don't properly setup WB MTRRs to
> > cover all available RAM, meaning the last few megs (or even gigs)
> > of memory will be marked uncached. Since Linux tends to allocate
> > from high memory addresses first, this causes the machine to be
> > unusably slow as soon as the kernel starts really using memory
> > (i.e. right around init time).
> >
> > This patch works around the problem by scanning the MTRRs at
> > boot and figuring out whether the current end_pfn value (setup
> > by early e820 code) goes beyond the highest WB MTRR range, and
> > if so, trimming it to match. A fairly obnoxious KERN_WARNING
> > is printed too, letting the user know that not all of their
> > memory is available due to a likely BIOS bug.
> >
> > Something similar could be done on i386 if needed, but the boot
> > ordering would be slightly different, since the MTRR code on i386
> > depends on the boot_cpu_data structure being setup.
> >
> > This patch incorporates the feedback from Eric and Andi:
> > - use MAX_VAR_RANGES instead of NUM_VAR_RANGES
> > - move array declaration to header file as an extern
> > - add command line disable option "disable_mtrr_trim"
> > - don't run the trim code if the MTRR default type is cacheable
> > - don't run the trim code on non-Intel machines
> >
> > Justin, feel free to test again if you have time and add your
> > "Tested-by" signoff.
> >
> > Andi, as for large pages, do you think this is ok as is, or should
> > I trim a larger granularity? If so, what granularity?
> >
> > Signed-off-by: Jesse Barnes <[email protected]>
> >
> > Thanks,
> > Jesse
>
> NAK.
>
> for AMD Rev F Opteron later CPU, BIOS will not set WB in MTRR for 4G
> above mem.
>
> This patch will get rid of those RAM.
Yeah, Eric already mentioned that. I'll rework it to only run on Intel
CPUs per Eric's last mail.
Thanks,
Jesse
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
