On Mon, Apr 21, 2014 at 12:29 AM, Jet Chen <jet.chen@intel.com> wrote:
> HI Dan,
>
> we noticed the below changes on
>
> git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata for-next
> commit 8a4aeec8d2d6a3edeffbdfae451cdf05cbf0fefd ("libata/ahci: accommodate
> tag ordered controllers")

Hi, was this on simulated hardware or a real AHCI controller and disk?

It does appear this test noticed increased throughput:

    203893 ~ 0%      +3.7%     211474 ~ 0%  TOTAL iostat.sda.wkB/s

I wonder if ap->last_tag can be moved to a hotter cacheline, but if
throughput goes up I can imagine it throws off the cpu statistics
quite a bit.