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 11:01:30 +0100 [thread overview]
Message-ID: <20161209100130.GS3174@twins.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:
> +static inline u64 mul_u32_u32(u32 a, u32 b)
> +{
> + u64 ret;
> +
> + asm ("mull %[b]" : "=A" (ret) : [a] "a" (a), [b] "g" (b) );
> +
> + return ret;
> +}
ARGH, that's broken on x86_64, it needs to be:
u32 high, low;
asm ("mull %[b]" : "=a" (low), "=d" (high)
: [a] "a" (a), [b] "g" (b) );
return low | ((u64)high) << 32;
The 'A' constraint doesn't work right.
And with that all the benchmark results are borken too.
root@ivb-ep:~/spinlocks# for i in -m64 -m32 -mx32 ; do echo $i; gcc -O3 $i -o mult mult.c -lm; ./mult; done
-m64
cond: avg: 7.474872 +- 0.008302
uncond: avg: 9.116401 +- 0.008468
128: avg: 0.826584 +- 0.005514
-m32
cond: avg: 16.604030 +- 0.009808
uncond: avg: 13.115470 +- 0.004452
-mx32
cond: avg: 6.168156 +- 0.006650
uncond: avg: 7.202092 +- 0.006813
128: avg: 0.081809 +- 0.008440
next prev parent reply other threads:[~2016-12-09 10:01 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
2016-12-09 10:01 ` Peter Zijlstra [this message]
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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