[PATCH V2] arm64: optimized copy_to_user and copy_from_user assembly code

Hi Feng,

On 2014?08?12? 02:05, Feng Kan wrote:

On Sun, Aug 10, 2014 at 8:01 PM, Radha Mohan [off-list ref] wrote:

quoted

Hi Feng,

quoted

+
+.Lcpy_not_short:
+       /*
+        * We don't much care about the alignment of DST, but we want SRC
+        * to be 128-bit (16 byte) aligned so that we don't cross cache line
+        * boundaries on both loads and stores.
+        */

Could you please tell why is destination alignment not an issue? Is
this a generic implementation that you are referring to or specific to
your platform?

This is per Linaro Cortext String optimization routines.

https://launchpad.net/cortex-strings

Zhichang submitted something similar for the memcpy from the
same optimization.

Sorry resend in text mode.

If the both dst and src are not aligned and their alignment offset are not equal, i haven't found better way
to handle.
But it is lucky ARMv8 support the non-align memory access.
At the beginning of my patch work, i also think maybe it is more better that all load or store are aligned. I
wrote the code just like the ARMv7 memcpy, firstly loaded the data from SRC and buffered them in several
registers and combined as a new word( 16 bytes), then stored it to the aligned DST. But the performance is a
bit worst.

~Zhichang

quoted

quoted

--
1.9.1


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