x86/mm: Rip out complicated, out-of-date, buggy TLB flushing

I think the flush_tlb_mm_range() code that tries to tune the
flush sizes based on the CPU needs to get ripped out for
several reasons:

1. It is obviously buggy.  It uses mm->total_vm to judge the
   task's footprint in the TLB.  It should certainly be using
   some measure of RSS, *NOT* ->total_vm since only resident
   memory can populate the TLB.
2. Haswell, and several other CPUs are missing from the
   intel_tlb_flushall_shift_set() function.  Thus, it has been
   demonstrated to bitrot quickly in practice.
3. It is plain wrong in my vm:
	[    0.037444] Last level iTLB entries: 4KB 0, 2MB 0, 4MB 0
	[    0.037444] Last level dTLB entries: 4KB 0, 2MB 0, 4MB 0
	[    0.037444] tlb_flushall_shift: 6
   Which leads to it to never use invlpg.
4. The assumptions about TLB refill costs are wrong:
	http://lkml.kernel.org/r/1337782555-8088-3-git-send-email-alex.shi@intel.com
    (more on this in later patches)
5. I can not reproduce the original data: https://lkml.org/lkml/2012/5/17/59
   I believe the sample times were too short.  Running the
   benchmark in a loop yields times that vary quite a bit.

Note that this leaves us with a static ceiling of 1 page.  This
is a conservative, dumb setting, and will be revised in a later
patch.

This also removes the code which attempts to predict whether we
are flushing data or instructions.  We expect instruction flushes
to be relatively rare and not worth tuning for explicitly.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: http://lkml.kernel.org/r/20140731154055.ABC88E89@viggo.jf.intel.com
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 0 insertions, 7 deletions

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index ce8b8ff0e0ef..a1a53d094987 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -741,11 +741,6 @@ static unsigned int amd_size_cache(struct cpuinfo_x86 *c, unsigned int size)
 }
 #endif
 
-static void cpu_set_tlb_flushall_shift(struct cpuinfo_x86 *c)
-{
-        tlb_flushall_shift = 6;
-}
-
 static void cpu_detect_tlb_amd(struct cpuinfo_x86 *c)
 {
         u32 ebx, eax, ecx, edx;
@@ -793,8 +788,6 @@ static void cpu_detect_tlb_amd(struct cpuinfo_x86 *c)
                 tlb_lli_2m[ENTRIES] = eax & mask;
 
         tlb_lli_4m[ENTRIES] = tlb_lli_2m[ENTRIES] >> 1;
-
-        cpu_set_tlb_flushall_shift(c);
 }
 
 static const struct cpu_dev amd_cpu_dev = {