From: John Stultz <john.stultz@linaro.org>
To: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Salman Qazi <sqazi@google.com>, Paul Turner <pjt@google.com>,
Tony Lindgren <tony@atomide.com>, Steven Miao <realmz6@gmail.com>,
lkml <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2] tile: avoid using clocksource_cyc2ns with absolute cycle count
Date: Wed, 16 Nov 2016 12:31:05 -0800 [thread overview]
Message-ID: <CALAqxLWyPOET2wqg7x+PddfNpORMUJYmCfpotN0BpxAQYOpbUw@mail.gmail.com> (raw)
In-Reply-To: <CALAqxLXywSrTLx7gTbouYptDBkpYhRGN3j7G-D3SE1DDF+K0dg@mail.gmail.com>
On Wed, Nov 16, 2016 at 12:29 PM, John Stultz <john.stultz@linaro.org> wrote:
> On Wed, Nov 16, 2016 at 12:16 PM, Chris Metcalf <cmetcalf@mellanox.com> wrote:
>> Change 4cecf6d401a0 results in essentially identical code for x86 as
>> this proposed change does for tile. In fact a follow-on change by
>> Salman introduced mult_frac() and switched to using it, so it was
>> identical at that point.
>>
>> PeterZ (cc'ed) then improved it to use __int128 math via
>> mul_u64_u32_shr(), but that doesn't help tile; we only do one multiply
>> instead of two, but the multiply is handled by an out-of-line call to
>> __multi3, and the sched_clock() function ends up about 2.5x slower as
>> a result.
>>
>> Thanks for thinking about this!
>
> Heh. Thanks for the history lesson and apologies for my forgetfulness. :)
Oh.. and some of these details might be useful to have in the commit message!
thanks
-john
next prev parent reply other threads:[~2016-11-16 20:31 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-16 16:57 [PATCH] clocksource_cyc2ns: avoid overflowing 64 bits Chris Metcalf
2016-11-16 18:04 ` John Stultz
2016-11-16 19:30 ` Chris Metcalf
2016-11-16 19:35 ` [PATCH v2] tile: avoid using clocksource_cyc2ns with absolute cycle count Chris Metcalf
2016-11-16 19:59 ` John Stultz
2016-11-16 20:16 ` Chris Metcalf
2016-11-16 20:29 ` John Stultz
2016-11-16 20:31 ` John Stultz [this message]
2016-11-17 9:53 ` Peter Zijlstra
2016-11-17 20:00 ` Chris Metcalf
2016-11-18 10:34 ` Peter Zijlstra
2016-11-18 14:24 ` Chris Metcalf
2016-11-18 14:50 ` Peter Zijlstra
2016-11-16 19:40 ` [PATCH] clocksource_cyc2ns: avoid overflowing 64 bits John Stultz
2016-11-16 19:45 ` John Stultz
2016-11-16 19:56 ` Chris Metcalf
2016-11-16 20:00 ` John Stultz
2016-11-16 20:30 ` Chris Metcalf
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