tree b62bf366bcd6b7133576ce519198bc3af8f54771
parent 8402b42312921ab0f819e324f468fd478e8c3708
author Chitti Babu Theegala <ctheegal@codeaurora.org> 1481834608 +0530
committer Christopher Ferris <cferris@google.com> 1484179150 -0800

Fix streaming(memcpy) performance on Cortex-A7

Stream-mode detection for L1 in A7-core is failing for
non cache-line-size (non 64 byte) aligned addresses.
This leads to destination data getting cached unnecessarily.
This A7 issue is confirmed by ARM

This issue is solved by aligning destination address to 64 byte before
entering the loop in memcpy routine.
Though we get lower score for micro_bench memcpy when L1 cache is bypassed,
it is desirable since it avoids unnecessary eviction of other process data
from L1 which is good for overall system performance.

Higher micro_bench memcpy numbers for < 64byte alignment shows good numbers
but this is at the cost of L1 cache pollution. During memcpy/memset,
unnecessary data is filled in L1 cache, this causes eviction of other
process data from L1.
For example during msmset(0), L1 cache gets filled with 0s which should be
avoided.

Additionally, there is another issue with cortex A7 that impacts performance
for all alignments / all Android Wear versions:
Store Buffer on A7 is 32 byte which limits the 32-byte back to back stores.
In the current implementation back to back 32bytes writes is causing CPU stalls.
This issue can be solved by interleaved Loads and Stores.
This helps in avoiding CPU stalls during memcpy by utilizing efficiently the
A7 internal load and store buffers.

Bug: 31917556

Change-Id: Ie5f12f2bb5d86f627686730416279057e4f5f6d0
(cherry picked from commit cbfdc7f9054e0bc8071aaf3a70afc00273a8a869)