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authorDave Hansen <dave.hansen@linux.intel.com>2014-07-31 19:40:55 +0400
committerH. Peter Anvin <hpa@linux.intel.com>2014-07-31 19:48:50 +0400
commite9f4e0a9fe2723078b7a1a1169828dd46a7b2f9e (patch)
treec16300d2f05f2fce6b7b70b2c6fed1ac58486129 /arch/x86/mm/tlb.c
parent4995ab9cf512e9a6cc07dfd6b1d4e2fc48ce7fef (diff)
downloadlinux-e9f4e0a9fe2723078b7a1a1169828dd46a7b2f9e.tar.xz
x86/mm: Rip out complicated, out-of-date, buggy TLB flushing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>
Diffstat (limited to 'arch/x86/mm/tlb.c')
-rw-r--r--arch/x86/mm/tlb.c87
1 files changed, 11 insertions, 76 deletions
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 378fbef279d2..dff6ddebc45f 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -158,13 +158,14 @@ void flush_tlb_current_task(void)
preempt_enable();
}
+/* in units of pages */
+unsigned long tlb_single_page_flush_ceiling = 1;
+
void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
unsigned long end, unsigned long vmflag)
{
- bool need_flush_others_all = true;
+ int need_flush_others_all = 1;
unsigned long addr;
- unsigned act_entries, tlb_entries = 0;
- unsigned long nr_base_pages;
preempt_disable();
if (current->active_mm != mm)
@@ -175,29 +176,16 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
goto out;
}
- if (end == TLB_FLUSH_ALL || tlb_flushall_shift == -1
- || vmflag & VM_HUGETLB) {
+ if (end == TLB_FLUSH_ALL || vmflag & VM_HUGETLB) {
local_flush_tlb();
goto out;
}
- /* In modern CPU, last level tlb used for both data/ins */
- if (vmflag & VM_EXEC)
- tlb_entries = tlb_lli_4k[ENTRIES];
- else
- tlb_entries = tlb_lld_4k[ENTRIES];
-
- /* Assume all of TLB entries was occupied by this task */
- act_entries = tlb_entries >> tlb_flushall_shift;
- act_entries = mm->total_vm > act_entries ? act_entries : mm->total_vm;
- nr_base_pages = (end - start) >> PAGE_SHIFT;
-
- /* tlb_flushall_shift is on balance point, details in commit log */
- if (nr_base_pages > act_entries) {
+ if ((end - start) > tlb_single_page_flush_ceiling * PAGE_SIZE) {
count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
local_flush_tlb();
} else {
- need_flush_others_all = false;
+ need_flush_others_all = 0;
/* flush range by one by one 'invlpg' */
for (addr = start; addr < end; addr += PAGE_SIZE) {
count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE);
@@ -259,68 +247,15 @@ static void do_kernel_range_flush(void *info)
void flush_tlb_kernel_range(unsigned long start, unsigned long end)
{
- unsigned act_entries;
- struct flush_tlb_info info;
-
- /* In modern CPU, last level tlb used for both data/ins */
- act_entries = tlb_lld_4k[ENTRIES];
/* Balance as user space task's flush, a bit conservative */
- if (end == TLB_FLUSH_ALL || tlb_flushall_shift == -1 ||
- (end - start) >> PAGE_SHIFT > act_entries >> tlb_flushall_shift)
-
+ if (end == TLB_FLUSH_ALL ||
+ (end - start) > tlb_single_page_flush_ceiling * PAGE_SIZE) {
on_each_cpu(do_flush_tlb_all, NULL, 1);
- else {
+ } else {
+ struct flush_tlb_info info;
info.flush_start = start;
info.flush_end = end;
on_each_cpu(do_kernel_range_flush, &info, 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 < -1 || shift >= BITS_PER_LONG)
- 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 __init create_tlb_flushall_shift(void)
-{
- 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