linux-kernel - Re: [PATCH] x86: mtrr cleanup for converting continuous to discrete

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Date:	Thu, 1 May 2008 10:40:40 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Mika Fischer" <mika.fischer@...pnet.de>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Gabriel C" <nix.or.die@...glemail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: mtrr cleanup for converting continuous to discrete - auto detect

On Thu, May 1, 2008 at 9:59 AM, Mika Fischer <mika.fischer@...pnet.de> wrote:
> Yinghai Lu schrieb:
>
>
> > On Thu, May 1, 2008 at 5:09 AM, Mika Fischer <mika.fischer@...pnet.de> wrote:
>  >> Yinghai Lu schrieb:
>  >>
>  >>> loop mtrr chunk_size and gran_size from 1M to 2G to find out optimal value.
>  >>  >
>  >>  > so user don't need to add mtrr_chunk_size and mtrr_gran_size,
>  >>  >
>  >>  > if optimal value is not found, print out all list to help select less optimal
>  >>  > value.
>  >>  >
>  >>  > add mtrr_spare_reg_nr= so user could set 2 instead of 1, if the card need more entries.
>  >>
>  >>  On my system x86-latest + this patch and using no boot options gives me
>  >>  this /proc/mtrr:
>  >>  reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
>  >>  reg01: base=0x80000000 (2048MB), size= 512MB: write-back, count=1
>  >>  reg02: base=0xa0000000 (2560MB), size= 256MB: write-back, count=1
>  >>  reg03: base=0xb0000000 (2816MB), size= 256MB: write-back, count=1
>  >>  reg04: base=0xbf700000 (3063MB), size=   1MB: uncachable, count=1
>  >>  reg05: base=0xbf800000 (3064MB), size=   8MB: uncachable, count=1
>  >>  reg06: base=0x100000000 (4096MB), size=1024MB: write-back, count=1
>  >>
>  >>  Which is OK. It could probably collapse reg01-reg03 into one but that's
>  >>  a minor issue (for me at least, there are probably cases where
>  >>  collapsing them might save the user from having to specify the
>  >>  mtrr_spare_reg_nr boot option).
>  >
>  > yes. please try mtrr_spare_reg_nr=3 or etc.
>
>  Sure this works. But that was my point exactly. It should be possible to
>  figure out the better configuration automatically so that I *don't* have
>  to specify mtrr_spare_reg_nr=3.
>
>  Or in other words: If there are multiple equivalent configurations that
>  don't lose any RAM(!), the one with the most free MTRR regs should be
>  preferred.
>
>  AFAICT you loop over the chunk size and stop when you have found a
>  configuration that leaves the number of free MTRR registers requested
>  (default 1).
>
>  This will almost always result in a configuration where you have
>  *exactly* the number of requested free regs available, even if a more
>  efficient configuration was possible.

OK, will send another version out.

YH
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