x86: Scale up the number of TLB invalidate vectors with NR_CPUs, up to 32

Make the maxium TLB invalidate vectors depend on NR_CPUS linearly,
with a maximum of 32 vectors.

We currently only have 8 vectors for TLB invalidation and that is clearly
inadequate. If we have a lot of CPUs, the CPUs need share the 8 vectors and
tlbstate_lock is used to protect them. flush_tlb_page() is
heavily used in page reclaim, which will cause a lot of lock
contention for tlbstate_lock.

Andi Kleen suggested increasing the vectors number to 32, which should be
good for current typical systems to reduce the tlbstate_lock contention.

My test system has 4 sockets and 64G memory, and 64 CPUs. My
workload creates 64 processes. Each process mmap reads a big
empty sparse file. The total size of the files are 2*total_mem,
so this will cause a lot of page reclaim.

Below is the result I get from perf call-graph profiling:

 without the patch:
 ------------------

    24.25%           usemem  [kernel]                                   [k] _raw_spin_lock
                     |
                     --- _raw_spin_lock
                        |
                        |--42.15%-- native_flush_tlb_others

 with the patch:
 ------------------

    14.96%           usemem  [kernel]                                   [k] _raw_spin_lock
                     |
                     --- _raw_spin_lock
                        |--13.89%-- native_flush_tlb_others

So this heavily reduces the tlbstate_lock contention.

Suggested-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1295232727.1949.709.camel@sli10-conroe>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 9 insertions, 4 deletions

diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 42f0d4a30f1b..4980f48bbbb7 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -17,8 +17,8 @@
  *  Vectors   0 ...  31 : system traps and exceptions - hardcoded events
  *  Vectors  32 ... 127 : device interrupts
  *  Vector  128         : legacy int80 syscall interface
- *  Vectors 129 ... 229 : device interrupts
- *  Vectors 230 ... 255 : special interrupts
+ *  Vectors 129 ... INVALIDATE_TLB_VECTOR_START-1 : device interrupts
+ *  Vectors INVALIDATE_TLB_VECTOR_START ... 255 : special interrupts
  *
  * 64-bit x86 has per CPU IDT tables, 32-bit has one shared IDT table.
  *
@@ -124,8 +124,13 @@
  */
 #define LOCAL_TIMER_VECTOR              0xef
 
-/* f0-f7 used for spreading out TLB flushes: */
-#define NUM_INVALIDATE_TLB_VECTORS         8
+/* up to 32 vectors used for spreading out TLB flushes: */
+#if NR_CPUS <= 32
+# define NUM_INVALIDATE_TLB_VECTORS NR_CPUS
+#else
+# define NUM_INVALIDATE_TLB_VECTORS 32
+#endif
+
 #define INVALIDATE_TLB_VECTOR_END       0xee
 #define INVALIDATE_TLB_VECTOR_START     \
         (INVALIDATE_TLB_VECTOR_END - NUM_INVALIDATE_TLB_VECTORS + 1)