x86/tlb: add tlb_flushall_shift knob into debugfs

kernel will replace cr3 rewrite with invlpg when
  tlb_flush_entries <= active_tlb_entries / 2^tlb_flushall_factor
if tlb_flushall_factor is -1, kernel won't do this replacement.

User can modify its value according to specific CPU/applications.

Thanks for Borislav providing the help message of
CONFIG_DEBUG_TLBFLUSH.

Signed-off-by: Alex Shi <alex.shi@intel.com>
Link: http://lkml.kernel.org/r/1340845344-27557-6-git-send-email-alex.shi@intel.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index e46c2147397f..b322f124ee3c 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -129,6 +129,25 @@ config DOUBLEFAULT
           option saves about 4k and might cause you much additional grey
           hair.
 
+config DEBUG_TLBFLUSH
+        bool "Set upper limit of TLB entries to flush one-by-one"
+        depends on DEBUG_KERNEL && (X86_64 || X86_INVLPG)
+        ---help---
+
+        X86-only for now.
+
+        This option allows the user to tune the amount of TLB entries the
+        kernel flushes one-by-one instead of doing a full TLB flush. In
+        certain situations, the former is cheaper. This is controlled by the
+        tlb_flushall_shift knob under /sys/kernel/debug/x86. If you set it
+        to -1, the code flushes the whole TLB unconditionally. Otherwise,
+        for positive values of it, the kernel will use single TLB entry
+        invalidating instructions according to the following formula:
+
+        flush_entries <= active_tlb_entries / 2^tlb_flushall_shift
+
+        If in doubt, say "N".
+
 config IOMMU_DEBUG
         bool "Enable IOMMU debugging"
         depends on GART_IOMMU && DEBUG_KERNEL