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

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Message-ID: <295ab33e-45da-af64-6716-c8f387a0cb20@mellanox.com>
Date:   Wed, 16 Nov 2016 14:56:07 -0500
From:   Chris Metcalf <cmetcalf@...lanox.com>
To:     John Stultz <john.stultz@...aro.org>
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 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?

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