linux-kernel - Re: [PATCH] clocksource_cyc2ns: avoid overflowing 64 bits

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Message-ID: <CALAqxLVTUkx4x6z=AmqWruhfX9L6R_MVZd+_uiGOoQU-fV-K-A@mail.gmail.com>
Date:   Wed, 16 Nov 2016 12:00:56 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Chris Metcalf <cmetcalf@...lanox.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Salman Qazi <sqazi@...gle.com>, Paul Turner <pjt@...gle.com>,
        Tony Lindgren <tony@...mide.com>,
        Steven Miao <realmz6@...il.com>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clocksource_cyc2ns: avoid overflowing 64 bits

On Wed, Nov 16, 2016 at 11:56 AM, Chris Metcalf <cmetcalf@...lanox.com> wrote:
> On 11/16/2016 2:45 PM, John Stultz wrote:
>>
>> On Wed, Nov 16, 2016 at 11:30 AM, Chris Metcalf <cmetcalf@...lanox.com>
>> wrote:
>>>
>>> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
>>> index 08398182f56e..5444429884b8 100644
>>> --- a/include/linux/clocksource.h
>>> +++ b/include/linux/clocksource.h
>>> @@ -171,6 +171,10 @@ static inline u32 clocksource_hz2mult(u32 hz, u32
>>> shift_constant)
>>>    *
>>>    * Converts cycles to nanoseconds, using the given mult and shift.
>>>    *
>>> + * The code is optimized for performance and not intended to work
>>> + * with absolute clocksource cycles, as it will easily overflow,
>>> + * but just intended for relative (delta) clocksource cycles.
>>> + *
>>>    * XXX - This could use some mult_lxl_ll() asm optimization
>>
>> Just as a heads up, it seems your working against an older kernel, as
>> this didn't apply. Its simple enough to fix up, so I'll do so, but in
>> the future, please submit patches against something close to Linus
>> HEAD.
>
>
> Oops, sorry; it wasn't version skew (I'm at v4.9-rc4) but whitespace damage.
> I assumed if I just pasted the patch into Thunderbird it would work, since
> it had
> no tabs.  But bizarrely, if I look at the patch in the mailer, it shows a
> two-space
> prefix, but when I save the email to a file, it has a three-space prefix.
> WTF?

Yea. Not many mailers can be trusted with sending patches. I'd
recommend git-send-email. :)

thanks
-john