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numa: Use LAST_CPUPID_SHIFT to calculate LAST_CPUPID_MASK

PATCH In review Srikar Dronamraju 2 participants 3 messages Mar 14, 2014 – Mar 15, 2014

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Srikar Dronamraju

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#0 lore raw

PATCH 1/1 numa: Use LAST_CPUPID_SHIFT to calculate LAST_CPUPID_MASK

LAST_CPUPID_MASK is calculated using LAST_CPUPID_WIDTH. However LAST_CPUPID_WIDTH itself can be 0. (when LAST_CPUPID_NOT_IN_PAGE_FLAGS is set). In such a case LAST_CPUPID_MASK turns out to be 0.

But with recent commit 1ae71d0319: (mm: numa: bugfix for LAST_CPUPID_NOT_IN_PAGE_FLAGS) if LAST_CPUPID_MASK is 0, page_cpupid_xchg_last() and page_cpupid_reset_last() causes page->_last_cpupid to be set to 0.

This causes performance regression. Its almost as if numa_balancing is off.

Fix LAST_CPUPID_MASK by using LAST_CPUPID_SHIFT instead of LAST_CPUPID_WIDTH.

Signed-off-by Srikar Dronamraju <[email protected]>
include/linux/mm.h +1 -1
index c1b7414..b9765bf 100644
@@ -684,7 +684,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 #define ZONES_MASK		((1UL << ZONES_WIDTH) - 1)
 #define NODES_MASK		((1UL << NODES_WIDTH) - 1)
 #define SECTIONS_MASK		((1UL << SECTIONS_WIDTH) - 1)
-#define LAST_CPUPID_MASK	((1UL << LAST_CPUPID_WIDTH) - 1)
+#define LAST_CPUPID_MASK	((1UL << LAST_CPUPID_SHIFT) - 1)
 #define ZONEID_MASK		((1UL << ZONEID_SHIFT) - 1)
 
 static inline enum zone_type page_zonenum(const struct page *page)

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#1 lore raw

Some performance numbers and perf stats with and without the fix.

(3.14-rc6)
----------
numa01

Performance counter stats for '/usr/bin/time -f %e %S %U %c %w -o start_bench.out -a ./numa01':

         12,27,462 cs                                                           [100.00%]
          2,41,957 migrations                                                   [100.00%]
       1,68,01,713 faults                                                       [100.00%]
    7,99,35,29,041 cache-misses
            98,808 migrate:mm_migrate_pages                                     [100.00%]

    1407.690148814 seconds time elapsed

numa02

Performance counter stats for '/usr/bin/time -f %e %S %U %c %w -o start_bench.out -a ./numa02':

            63,065 cs                                                           [100.00%]
            14,364 migrations                                                   [100.00%]
          2,08,118 faults                                                       [100.00%]
      25,32,59,404 cache-misses
                12 migrate:mm_migrate_pages                                     [100.00%]

      63.840827219 seconds time elapsed

(3.14-rc6 with fix)
-------------------
numa01

Performance counter stats for '/usr/bin/time -f %e %S %U %c %w -o start_bench.out -a ./numa01':

          9,68,911 cs                                                           [100.00%]
          1,01,414 migrations                                                   [100.00%]
         88,38,697 faults                                                       [100.00%]
    4,42,92,51,042 cache-misses
          4,25,060 migrate:mm_migrate_pages                                     [100.00%]

     685.965331189 seconds time elapsed

numa02

Performance counter stats for '/usr/bin/time -f %e %S %U %c %w -o start_bench.out -a ./numa02':

            17,543 cs                                                           [100.00%]
             2,962 migrations                                                   [100.00%]
          1,17,843 faults                                                       [100.00%]
      11,80,61,644 cache-misses
            12,358 migrate:mm_migrate_pages                                     [100.00%]

      20.380132343 seconds time elapsed
Signature · 8 lines
Thanks and Regards
Srikar Dronamraju

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Reviewed-by on v1 1/1
#2 lore raw
In reply to Srikar Dronamraju
Quoted 9 lines · Srikar Dronamraju

LAST_CPUPID_MASK is calculated using LAST_CPUPID_WIDTH. However LAST_CPUPID_WIDTH itself can be 0. (when LAST_CPUPID_NOT_IN_PAGE_FLAGS is set). In such a case LAST_CPUPID_MASK turns out to be 0.

But with recent commit 1ae71d0319: (mm: numa: bugfix for LAST_CPUPID_NOT_IN_PAGE_FLAGS) if LAST_CPUPID_MASK is 0, page_cpupid_xchg_last() and page_cpupid_reset_last() causes page->_last_cpupid to be set to 0.

Quoted 7 lines

This causes performance regression. Its almost as if numa_balancing is off.

Fix LAST_CPUPID_MASK by using LAST_CPUPID_SHIFT instead of LAST_CPUPID_WIDTH.

Signed-off-by Srikar Dronamraju <[email protected]>
Reviewed-by Aneesh Kumar K.V <[email protected]>
Quoted 16 lines
include/linux/mm.h +1 -2
index c1b7414..b9765bf 100644
@@ -684,7 +684,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 #define ZONES_MASK		((1UL << ZONES_WIDTH) - 1)
 #define NODES_MASK		((1UL << NODES_WIDTH) - 1)
 #define SECTIONS_MASK		((1UL << SECTIONS_WIDTH) - 1)
-#define LAST_CPUPID_MASK	((1UL << LAST_CPUPID_WIDTH) - 1)
+#define LAST_CPUPID_MASK	((1UL << LAST_CPUPID_SHIFT) - 1)
 #define ZONEID_MASK		((1UL << ZONEID_SHIFT) - 1)
 
 static inline enum zone_type page_zonenum(const struct page *page)
 
--
Quoted 4 lines

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