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Commit 3df3212f authored by Alex Shi's avatar Alex Shi Committed by H. Peter Anvin
Browse files

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: default avatarAlex Shi <alex.shi@intel.com>
Link: http://lkml.kernel.org/r/1340845344-27557-6-git-send-email-alex.shi@intel.com


Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent c4211f42

arch/x86/Kconfig.debug

+19 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/mm/tlb.c

+51 −0
Original line number Diff line number Diff line
@@ -12,6 +12,7 @@ 
#include <asm/cache.h>

#include <asm/apic.h>

#include <asm/uv/uv.h>

#include <linux/debugfs.h>



DEFINE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate)

			= { &init_mm, 0, };
@@ -430,3 +431,53 @@ void flush_tlb_all(void) 
{

	on_each_cpu(do_flush_tlb_all, NULL, 1);

}



#ifdef CONFIG_DEBUG_TLBFLUSH

static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,

			     size_t count, loff_t *ppos)

{

	char buf[32];

	unsigned int len;



	len = sprintf(buf, "%hd\n", tlb_flushall_shift);

	return simple_read_from_buffer(user_buf, count, ppos, buf, len);

}



static ssize_t tlbflush_write_file(struct file *file,

		 const char __user *user_buf, size_t count, loff_t *ppos)

{

	char buf[32];

	ssize_t len;

	s8 shift;



	len = min(count, sizeof(buf) - 1);

	if (copy_from_user(buf, user_buf, len))

		return -EFAULT;



	buf[len] = '\0';

	if (kstrtos8(buf, 0, &shift))

		return -EINVAL;



	if (shift > 64)

		return -EINVAL;



	tlb_flushall_shift = shift;

	return count;

}



static const struct file_operations fops_tlbflush = {

	.read = tlbflush_read_file,

	.write = tlbflush_write_file,

	.llseek = default_llseek,

};



static int __cpuinit create_tlb_flushall_shift(void)

{

	if (cpu_has_invlpg) {

		debugfs_create_file("tlb_flushall_shift", S_IRUSR | S_IWUSR,

			arch_debugfs_dir, NULL, &fops_tlbflush);

	}

	return 0;

}

late_initcall(create_tlb_flushall_shift);

#endif