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

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Message-ID: <CAHp75VdTPzTK-MgrqU0N43YaNrwpN4pq8PwKAkcFQ-y_n6ez2A@mail.gmail.com>
Date:   Tue, 20 Mar 2018 15:44:46 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Rahul Lakkireddy <rahul.lakkireddy@...lsio.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 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?

-- 
With Best Regards,
Andy Shevchenko