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Subject[RFC 3/4]x86: make tlb invalidate vector number configurable
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Make the maxium TLB invalidate vectors depend on NR_CPUS, and the maxium
number is 32.
we currently only have 8 vectors for TLB invalidate. 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
suggests 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:
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.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
arch/x86/include/asm/irq_vectors.h | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

Index: linux/arch/x86/include/asm/irq_vectors.h
===================================================================
--- linux.orig/arch/x86/include/asm/irq_vectors.h 2010-11-02 14:41:01.000000000 +0800
+++ linux/arch/x86/include/asm/irq_vectors.h 2010-11-02 14:52:10.000000000 +0800
@@ -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 32
+#else
+#define NUM_INVALIDATE_TLB_VECTORS NR_CPUS
+#endif
+
#define INVALIDATE_TLB_VECTOR_END 0xee
#define INVALIDATE_TLB_VECTOR_START \
(INVALIDATE_TLB_VECTOR_END - NUM_INVALIDATE_TLB_VECTORS + 1)



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