iommu_gas: speed up augmentation

[dougm]

Summary

Rewrite iommu_gas_augment_entry to be 32 bytes smaller, after compilation, and a bit faster.

Test Plan

A copy of the original and modified code is included in this test program:

rb_toy.c6 KBDownload

, which is used to randomly insert and remove nodes while maintaining augmentation info. The change produces a measurable improvement.

x times.orig
+ times
+-------------------------------------------------------------------------------------+
|                 +    +    +     +                 x                               x |
|                +++  +++   +    +++x       x x     x  +    xxxxx                  xxx|
|++  +      ++   +++ ++++ +++    +++x ++    *xxx  x **++x  xxxxxx  x  x       xx  xxxx|
|             |__________M__A____________|     |_____________MA______________|        |
+-------------------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  40     87.234735     89.271164     88.287936     88.333866    0.61713185
+  40     85.813025      88.02519     86.803171     86.911903    0.56699337
Difference at 99.5% confidence
        -1.42196 +/- 0.42376
        -1.60976% +/- 0.479726%
        (Student's t, pooled s = 0.592593)