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

From: Rahul Lakkireddy <[email-masked]>
Date: Wed, 21 Mar 2018 17:57:09 +0530

On Tuesday, March 03/20/18, 2018 at 19:14:46 +0530, Andy Shevchenko wrote:
> On Tue, Mar 20, 2018 at 3:32 PM, Rahul Lakkireddy
> <[email-masked]> wrote:
> > On Monday, March 03/19/18, 2018 at 20:13:10 +0530, Thomas Gleixner wrote:
> >> On Mon, 19 Mar 2018, Rahul Lakkireddy wrote:
> 
> >> 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?
> 

We see same improvement when collecting logs while running
heavy IO with iozone.

Thanks,
Rahul