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SubjectRe: [RFC] Cachemap for 2.6.12rc4-mm1. Was Re: [PATCH] enhance x86 MTRR handling
Hi Andi,

On Fri, May 13, 2005 at 03:29:45PM +0200, Andi Kleen wrote:

> For memory (pfn_valid == 1) it would be more memory efficient to use a few bits
> in struct page->flags


> In general because there are lots of uses of "range lists" it would be better
> to put it as a library into lib.


> Coding style needs some work.


> Too many printks.

At least whilst this is getting polished, its worth keeping these
around. Once its stable, I agree, they can go (or at least be
demoted to dprintk's). It seems that theres some problems with
the current code, so they're definitly useful..

for eg..

CMAP: cmap_request_range: 0xf8000000 - 0xf8100fff (1)
CMAP: cachings mismatch (4 != 1)
CMAP: cmap_request_range: 0xf8101000 - 0xf8101fff (1)
CMAP: cachings mismatch (4 != 1)
CMAP: cmap_request_range: 0xf8102000 - 0xf8301fff (1)
CMAP: cachings mismatch (4 != 1)
[drm:radeon_do_init_cp] *ERROR* could not find ioremap agp regions!
CMAP: cmap_release_range: 0xff8f0000 - 0xff96efff
CMAP: last user, freeing
CMAP: last user, freeing
CMAP: release_range successful!!

I'm not sure where that's coming from yet. There's also a few
failures to release regions which need to be double checked.

> I am not sure yet the cmaps don't need reference counting. For some
> cases (user space support) they probably will.

Asides from cmap_entry->count ?
Hmm, there doesn't seem to be anything guarding concurrent accesses
to that.

> Need user space support, e.g. using the existing ioctls for /proc/bus/pci/*
> (they are currently not implemented on i386/x86-64 but should with this)
> Then someone would need to change the X server to use this.

By hooking into ioremap(), we're getting this done automatically.

01:00.0 VGA compatible controller: ATI Technologies Inc Radeon RV200 QW [Radeon 7500] (prog-if 00 [VGA])
Subsystem: PC Partner Limited RV200 QW [Radeon 7500 LE]
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping+ SERR+ FastB2B-
Status: Cap+ 66Mhz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR-
Latency: 32 (2000ns min), Cache Line Size 08
Interrupt: pin A routed to IRQ 225
Region 0: Memory at e8000000 (32-bit, prefetchable) [size=128M]
Region 1: I/O ports at c800 [size=256]
Region 2: Memory at ff8f0000 (32-bit, non-prefetchable) [size=64K]
Expansion ROM at ff8c0000 [disabled] [size=128K]
Capabilities: <available only to root>

(10:39:17:davej@dhcp83-2:~)$ grep e8000000 /proc/cachemap
0xe8000000 - 0xebffffff: 0x0004 1

Though I agree a userspace interface could be useful.

> Need to figure out if CMAP_ALLOW_OVERLAPPING should be set or not.

*nod*, and if it should, lose the ifdef completely.

> Probably need to go over the combining rule etc. with a fine comb

agreed. There's a bunch of errata on older CPUs that should probably
be checked too.

Thanks for the comments. I'm not working on this full-time, but
I'll continue to poke at it occasionally, especially if theres
interest from anyone else.

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