Eric Lee / linux-smarc-t335x-v3.2

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Commit f68e14805085972b4e0b0ab684af37f713b9c262

Authored by Michael S. Tsirkin
Committed by Linus Torvalds
1 parent 3d2d827f5c
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

mm: reduce atomic use on use_mm fast path 

When the mm being switched to matches the active mm, we don't need to
increment and then drop the mm count.  In a simple benchmark this happens
in about 50% of time.  Making that conditional reduces contention on that
cacheline on SMP systems.

Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 1 changed file with 6 additions and 3 deletions Side-by-side Diff

... ... @@ -26,13 +26,16 @@
26 26  
27 27 task_lock(tsk);
28 28 active_mm = tsk->active_mm;
29   - atomic_inc(&mm->mm_count);
  29 + if (active_mm != mm) {
  30 + atomic_inc(&mm->mm_count);
  31 + tsk->active_mm = mm;
  32 + }
30 33 tsk->mm = mm;
31   - tsk->active_mm = mm;
32 34 switch_mm(active_mm, mm, tsk);
33 35 task_unlock(tsk);
34 36  
35   - mmdrop(active_mm);
  37 + if (active_mm != mm)
  38 + mmdrop(active_mm);
36 39 }
37 40  
38 41 /*