From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
John Stultz <john.stultz@linaro.org>,
Ingo Molnar <mingo@kernel.org>,
David Gibson <david@gibson.dropbear.id.au>,
Liav Rehana <liavr@mellanox.com>,
Chris Metcalf <cmetcalf@mellanox.com>,
Richard Cochran <richardcochran@gmail.com>,
Parit Bhargava <prarit@redhat.com>,
Laurent Vivier <lvivier@redhat.com>,
"Christopher S. Hall" <christopher.s.hall@intel.com>
Subject: Re: [patch 5/6] [RFD] timekeeping: Provide optional 128bit math
Date: Fri, 9 Dec 2016 10:11:49 +0100 [thread overview]
Message-ID: <20161209091149.GE15765@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20161209083011.GD15765@worktop.programming.kicks-ass.net>
On Fri, Dec 09, 2016 at 09:30:11AM +0100, Peter Zijlstra wrote:
> > > Just for giggles, on tilegx the branch is actually slower than doing the
> > > mult unconditionally.
> > >
> > > The problem is that the two multiplies would otherwise completely
> > > pipeline, whereas with the conditional you serialize them.
> Only when using x86_64 instructions, once I fixed the i386 variant it
> was slower, probably due to register pressure and the like.
OK, maybe I messed up on i386, although I've yet to try running that on
an actual 32bit machine. I also need to dig up a small core, who knows
what atoms do.
Results are in cycles, average over 1e6 loops. I think the 128 results
are around 1 cycle, measurements are maybe a tad wobbly because I
compare against an empty loop to correct measurement overhead.
root@ivb-ep:~/tmp# for i in -m64 -m32 -mx32; do echo $i ; gcc -O3 $i -o mult mult.c -lm; ./mult ; done
-m64
cond: avg: 5.487738 +- 0.004152
uncond: avg: 4.495690 +- 0.006009
128: avg: 0.634496 +- 0.004795
-m32
cond: avg: 14.807630 +- 0.006890
uncond: avg: 11.601985 +- 0.009722
-mx32
cond: avg: 5.027696 +- 0.005766
uncond: avg: 4.038013 +- 0.008069
128: avg: 0.009928 +- 0.005730
root@hsw:~/tmp# for i in -m64 -m32 -mx32; do echo $i ; gcc -O3 $i -o mult mult.c -lm; ./mult ; done
-m64
cond: avg: 1.998718 +- 0.008775
uncond: avg: 2.004795 +- 0.009865
128: avg: 0.991947 +- 0.007607
-m32
cond: avg: 12.981868 +- 0.011239
uncond: avg: 13.000566 +- 0.011668
-mx32
cond: avg: 2.005437 +- 0.006840
uncond: avg: 3.001631 +- 0.004786
128: avg: 1.990425 +- 0.003880
next prev parent reply other threads:[~2016-12-09 9:12 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 20:49 [patch 0/6] timekeeping: Cure the signed/unsigned wreckage Thomas Gleixner
2016-12-08 20:49 ` [patch 1/6] timekeeping: Force unsigned clocksource to nanoseconds conversion Thomas Gleixner
2016-12-08 23:38 ` David Gibson
2016-12-09 11:13 ` [tip:timers/core] timekeeping_Force_unsigned_clocksource_to_nanoseconds_conversion tip-bot for Thomas Gleixner
2016-12-08 20:49 ` [patch 2/6] timekeeping: Make the conversion call chain consistently unsigned Thomas Gleixner
2016-12-08 23:39 ` David Gibson
2016-12-09 11:13 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2016-12-08 20:49 ` [patch 3/6] timekeeping: Get rid of pointless typecasts Thomas Gleixner
2016-12-08 23:40 ` David Gibson
2016-12-09 11:14 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2016-12-08 20:49 ` [patch 4/6] timekeeping: Use mul_u64_u32_shr() instead of open coding it Thomas Gleixner
2016-12-08 23:41 ` David Gibson
2016-12-09 11:14 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2016-12-08 20:49 ` [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Thomas Gleixner
2016-12-09 4:08 ` Ingo Molnar
2016-12-09 4:29 ` Ingo Molnar
2016-12-09 4:39 ` John Stultz
2016-12-09 4:48 ` Peter Zijlstra
2016-12-09 5:22 ` Ingo Molnar
2016-12-09 5:41 ` Peter Zijlstra
2016-12-09 5:11 ` Peter Zijlstra
2016-12-09 6:08 ` Peter Zijlstra
2016-12-09 5:26 ` Peter Zijlstra
2016-12-09 6:38 ` Peter Zijlstra
2016-12-09 8:30 ` Peter Zijlstra
2016-12-09 9:11 ` Peter Zijlstra [this message]
2016-12-09 10:01 ` Peter Zijlstra
2016-12-09 17:32 ` Chris Metcalf
2017-01-14 12:51 ` [tip:timers/core] math64, timers: Fix 32bit mul_u64_u32_shr() and friends tip-bot for Peter Zijlstra
2016-12-09 10:18 ` [patch 5/6] [RFD] timekeeping: Provide optional 128bit math Peter Zijlstra
2016-12-09 17:20 ` Chris Metcalf
2016-12-08 20:49 ` [patch 6/6] [RFD] timekeeping: Get rid of cycle_t Thomas Gleixner
2016-12-08 23:43 ` David Gibson
2016-12-09 4:52 ` [patch 0/6] timekeeping: Cure the signed/unsigned wreckage John Stultz
2016-12-09 5:30 ` Peter Zijlstra
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