Re: [RFC PATCH 2/3] x86/io: implement 256-bit IO read and write

On Tue, Mar 20, 2018 at 3:32 PM, Rahul Lakkireddy
[off-list ref] wrote:

On Monday, March 03/19/18, 2018 at 20:13:10 +0530, Thomas Gleixner wrote:

quoted

On Mon, 19 Mar 2018, Rahul Lakkireddy wrote:

quoted

Aside of that I very much doubt that this is faster than 4 consecutive
64bit reads/writes as you have the full overhead of
kernel_fpu_begin()/end() for each access.

You did not provide any numbers for this so its even harder to
determine.

Sorry about that.  Here are the numbers with and without this series.

When reading up to 2 GB on-chip memory via MMIO, the time taken:

Without Series        With Series
(64-bit read)         (256-bit read)

52 seconds            26 seconds

As can be seen, we see good improvement with doing 256-bits at a
time.

But this is kinda synthetic test, right?
If you run in a normal use case where kernel not only collecting logs,
but doing something else, especially with frequent userspace
interaction, would be trend the same?

-- 
With Best Regards,
Andy Shevchenko