linux-kernel - MTRR cleanup does not kick in

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Date:	Sat, 17 Mar 2012 07:36:39 +0100
From:	Michael Reinelt <michael@...nelt.co.at>
To:	lkml <linux-kernel@...r.kernel.org>
Subject: MTRR cleanup does not kick in

Hi there,

I am (again) suffering from:
kernel: mtrr: no more MTRRs available
kernel: [drm] MTRR allocation failed.  Graphics performance may suffer.

kernel is vanilla 3.2.11

I know that this *used* to work, but I had to specify mtrr_gran_size=16M mtrr_chunk_size=128M on the kernel command line.

Now, with the current kernel, I could not find *any* MTRR cleanup debug messages at all.

I debugged a bit, and probably found the cause:

arch/x86/kernel/cpu/mtrr/cleanup.c:mtrr_need_cleanup(void)

/* Check if we only had WB and UC */
if (num[MTRR_TYPE_WRBACK] + num[MTRR_TYPE_UNCACHABLE] !=
     num_var_ranges - num[MTRR_NUM_TYPES])
	return 0;

This one kicks in, and disables the MTRR cleanup, resulting in all 10 MTRR registers in use, and no more MTRRs available 
for DRM.

I disabled this check, and now the MTRR cleaner works fine, even finding a optimal value for my system with only 9 
registers, leaving one available for DRM.

maybe the mtrr_need_cleanup() function should take nr_mtrr_spare_reg into account?

regards, Michael

PS please keep me on CC as I'm not subscribed. thanks!

-- 
Michael Reinelt <michael@...nelt.co.at>
http://home.pages.at/reinelt
GPG-Key 0xDF13BA50
ICQ #288386781
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