linux-kernel - Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math

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Message-ID: <3f7101ba-5693-c98b-b319-9bab81b151fc@mellanox.com>
Date:   Fri, 9 Dec 2016 12:20:52 -0500
From:   Chris Metcalf <cmetcalf@...lanox.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     LKML <linux-kernel@...r.kernel.org>,
        John Stultz <john.stultz@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Liav Rehana <liavr@...lanox.com>,
        Richard Cochran <richardcochran@...il.com>,
        Parit Bhargava <prarit@...hat.com>,
        Laurent Vivier <lvivier@...hat.com>,
        "Christopher S. Hall" <christopher.s.hall@...el.com>
Subject: Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math

On 12/9/2016 5:18 AM, Peter Zijlstra wrote:
> On Fri, Dec 09, 2016 at 07:38:47AM +0100, Peter Zijlstra wrote:
>
>> Turns out using GCC-6.2.1 we have the same problem on i386, GCC doesn't
>> recognise the 32x32 mults and generates crap.
>>
>> This used to work :/
> I tried:
>
> gcc-4.4: good
> gcc-4.6, gcc-4.8, gcc-5.4, gcc-6.2: bad

I also found 4.4 was good on tilegx at recognizing the 32x32, and bad on
the later versions I tested; I don't recall which specific later versions I
tried, though.

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com