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x86/tlb: add tlb_flushall_shift knob into debugfs

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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>
This commit is contained in:
Alex Shi 2012-06-28 09:02:20 +08:00 committed by H. Peter Anvin
parent c4211f42d3
commit 3df3212f97
2 changed files with 70 additions and 0 deletions
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19
arch/x86/Kconfig.debug
View File

@ -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

51
arch/x86/mm/tlb.c
View File

@ -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