From: "George Spelvin" <linux@horizon.com>
To: linux@horizon.com, tytso@mit.edu
Cc: hpa@linux.intel.com, linux-kernel@vger.kernel.org,
mingo@kernel.org, price@mit.edu
Subject: Re: random: Benchamrking fast_mix2
Date: 14 Jun 2014 01:25:27 -0400 [thread overview]
Message-ID: <20140614052527.14849.qmail@ns.horizon.com> (raw)
In-Reply-To: <20140614030621.GB6447@thunk.org>
> At least for Intel, between its branch predictor and speculative
> execution engine, it doesn't make a difference.
*Sigh*. We need live measurement. My testing (in your test
harness!) showed a noticeable (~10%) speedup.
> When I did a quick comparison of your 64-bit fast_mix2 variant, it's
> much slower than either the 32-bit fast_mix2, or the original fast_mix
> alrogithm.
That is f***ing *bizarre*. For me, it's *significantly* faster.
You *are* compiling -m64, right? Because I agree with you it'd
be stupid to try to use it on 32-bit machines.
Forcing max-speed CPU:
# ./perftest ./ted64
fast_mix: 419 fast_mix2: 419 fast_mix4: 318
fast_mix: 386 fast_mix2: 419 fast_mix4: 112
fast_mix: 419 fast_mix2: 510 fast_mix4: 328
fast_mix: 420 fast_mix2: 510 fast_mix4: 306
fast_mix: 420 fast_mix2: 510 fast_mix4: 317
fast_mix: 419 fast_mix2: 510 fast_mix4: 318
fast_mix: 362 fast_mix2: 510 fast_mix4: 317
fast_mix: 420 fast_mix2: 510 fast_mix4: 306
fast_mix: 419 fast_mix2: 499 fast_mix4: 318
fast_mix: 420 fast_mix2: 510 fast_mix4: 328
And not:
$ ./ted64
fast_mix: 328 fast_mix2: 430 fast_mix4: 272
fast_mix: 442 fast_mix2: 442 fast_mix4: 272
fast_mix: 442 fast_mix2: 430 fast_mix4: 272
fast_mix: 329 fast_mix2: 442 fast_mix4: 272
fast_mix: 329 fast_mix2: 430 fast_mix4: 272
fast_mix: 328 fast_mix2: 442 fast_mix4: 272
fast_mix: 329 fast_mix2: 431 fast_mix4: 272
fast_mix: 328 fast_mix2: 442 fast_mix4: 272
fast_mix: 328 fast_mix2: 431 fast_mix4: 272
fast_mix: 329 fast_mix2: 442 fast_mix4: 272
And on a Phenom:
$ /tmp/ted64
fast_mix: 250 fast_mix2: 174 fast_mix4: 109
fast_mix: 258 fast_mix2: 170 fast_mix4: 114
fast_mix: 371 fast_mix2: 285 fast_mix4: 109
fast_mix: 516 fast_mix2: 156 fast_mix4: 90
fast_mix: 140 fast_mix2: 184 fast_mix4: 170
fast_mix: 406 fast_mix2: 146 fast_mix4: 88
fast_mix: 185 fast_mix2: 114 fast_mix4: 94
fast_mix: 161 fast_mix2: 116 fast_mix4: 98
fast_mix: 152 fast_mix2: 104 fast_mix4: 94
fast_mix: 352 fast_mix2: 140 fast_mix4: 79
> So given that 32-bit processors tend to be slower, I'm pretty sure
> if we want to add a 64-bit optimization, we'll have to conditionalize
> it on BITS_PER_LONG == 64 and include both the original code and the
> 64-bit optimized code.
Sorry I neglected to say so earlier; that has *always* been my intention.
The 32-bit version is primary; the 64-bit version is a conditional
optimization.
If I can make it faster *and* have more avalanche (and less register
pressure, too), it seems worth the hassle of having two versions.
next prev parent reply other threads:[~2014-06-14 5:25 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-09 0:05 [RFC PATCH] drivers/char/random.c: Is reducing locking range like this safe? George Spelvin
2014-06-09 1:35 ` Theodore Ts'o
2014-06-09 2:10 ` George Spelvin
2014-06-09 2:18 ` George Spelvin
2014-06-09 4:03 ` George Spelvin
2014-06-09 9:23 ` George Spelvin
2014-06-09 13:34 ` Theodore Ts'o
2014-06-09 15:04 ` George Spelvin
2014-06-09 15:50 ` Theodore Ts'o
2014-06-09 16:11 ` George Spelvin
2014-06-10 0:20 ` drivers/char/random.c: more ruminations George Spelvin
2014-06-10 1:20 ` Theodore Ts'o
2014-06-10 3:10 ` George Spelvin
2014-06-10 15:25 ` Theodore Ts'o
2014-06-10 20:40 ` George Spelvin
2014-06-10 21:20 ` Theodore Ts'o
2014-06-11 0:10 ` George Spelvin
2014-06-11 2:08 ` Theodore Ts'o
2014-06-11 3:58 ` George Spelvin
2014-06-11 13:11 ` Theodore Ts'o
2014-06-12 0:42 ` George Spelvin
2014-06-12 1:03 ` H. Peter Anvin
2014-06-11 4:34 ` George Spelvin
2014-06-11 13:09 ` Theodore Ts'o
2014-06-11 2:21 ` Theodore Ts'o
2014-06-09 13:17 ` drivers/char/random.c: More futzing about George Spelvin
2014-06-11 16:38 ` Theodore Ts'o
2014-06-11 16:48 ` H. Peter Anvin
2014-06-11 19:25 ` Theodore Ts'o
2014-06-11 20:41 ` H. Peter Anvin
2014-06-12 0:44 ` H. Peter Anvin
2014-06-12 1:51 ` George Spelvin
2014-06-12 0:32 ` George Spelvin
2014-06-12 3:22 ` Theodore Ts'o
2014-06-12 4:13 ` random: Benchamrking fast_mix2 George Spelvin
2014-06-12 11:18 ` George Spelvin
2014-06-12 20:17 ` Theodore Ts'o
2014-06-12 20:46 ` Theodore Ts'o
2014-06-13 0:23 ` George Spelvin
2014-06-13 15:52 ` Theodore Ts'o
2014-06-14 2:10 ` George Spelvin
2014-06-14 3:06 ` Theodore Ts'o
2014-06-14 5:25 ` George Spelvin [this message]
2014-06-14 6:24 ` Theodore Ts'o
2014-06-14 8:03 ` George Spelvin
2014-06-14 11:14 ` George Spelvin
2014-06-14 15:13 ` George Spelvin
2014-06-14 16:33 ` Theodore Ts'o
2014-06-15 0:23 ` George Spelvin
2014-06-15 1:17 ` Theodore Ts'o
2014-06-15 6:58 ` George Spelvin
2014-06-15 13:01 ` Theodore Ts'o
2014-06-14 6:27 ` Theodore Ts'o
2014-06-14 4:55 ` [RFC] random: is the IRQF_TIMER test working as intended? George Spelvin
2014-06-14 6:43 ` Theodore Ts'o
2014-06-14 7:23 ` George Spelvin
2014-06-12 3:43 ` drivers/char/random.c: More futzing about George Spelvin
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