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

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Date:   Wed, 21 Mar 2018 17:57:09 +0530
From:   Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        Ganesh GR <ganeshgr@...lsio.com>,
        Nirranjan Kirubaharan <nirranjan@...lsio.com>,
        Indranil Choudhury <indranil@...lsio.com>
Subject: Re: [RFC PATCH 2/3] x86/io: implement 256-bit IO read and write

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
> <rahul.lakkireddy@...lsio.com> 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