From: "Jan Beulich" <JBeulich@suse.com>
To: "Ingo Molnar" <mingo@elte.hu>
Cc: <tglx@linutronix.de>, "Andrew Morton" <akpm@linux-foundation.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
<linux-kernel@vger.kernel.org>, <hpa@zytor.com>
Subject: Re: [PATCH] x86-64: fix memset() to support sizes of 4Gb and above
Date: Wed, 18 Jan 2012 10:40:33 +0000 [thread overview]
Message-ID: <4F16AFB1020000780006D671@nat28.tlf.novell.com> (raw)
In-Reply-To: <20120106110519.GA32673@elte.hu>
>>> On 06.01.12 at 12:05, Ingo Molnar <mingo@elte.hu> wrote:
>> * Jan Beulich <JBeulich@suse.com> wrote:
> Would be nice to add support for arch/x86/lib/memset_64.S as
> well, and look at the before/after performance of it.
Got this done, will post the patch soon. However, ...
> For example the kernel's memcpy routine in slightly faster than
> glibc's:
This is an illusion - since the kernel's memcpy_64.S also defines a
"memcpy" (not just "__memcpy"), the static linker resolves the
reference from mem-memcpy.c against this one. Apparent
performance differences rather point at effects like (guessing)
branch prediction (using the second vs the first entry of
routines[]). After fixing this, on my Westmere box glibc's is quite
a bit slower than the unrolled kernel variant (4% fewer
instructions, but about 15% more cycles).
> If such measurements all suggests equal or better performance,
> and if there's no erratum in current CPUs that would make 4G
> string copies dangerous [which your research suggests should be
> fine], i have no principal objection against this patch.
If I interpreted things correctly, there's a tiny win with the changes
(also for not-yet-posted memcpy equivalent):
# Original 3.2:
Performance counter stats for 'perf bench mem memcpy -r x86-64-unrolled' (1000 runs):
5,237,848 instructions # 1.01 insns per cycle ( +- 0.01% )
5,187,712 cycles # 0.000 GHz ( +- 0.10% )
0.003426133 seconds time elapsed ( +- 0.30% )
5,236,075 instructions # 1.01 insns per cycle ( +- 0.01% )
5,177,677 cycles # 0.000 GHz ( +- 0.08% )
0.003423426 seconds time elapsed ( +- 0.29% )
5,236,887 instructions # 1.01 insns per cycle ( +- 0.01% )
5,180,640 cycles # 0.000 GHz ( +- 0.08% )
0.003410956 seconds time elapsed ( +- 0.32% )
Performance counter stats for 'perf bench mem memset -r x86-64-unrolled' (1000 runs):
4,300,600 instructions # 0.97 insns per cycle ( +- 0.02% )
4,442,449 cycles # 0.000 GHz ( +- 0.12% )
0.002976608 seconds time elapsed ( +- 0.29% )
4,300,542 instructions # 0.97 insns per cycle ( +- 0.02% )
4,443,480 cycles # 0.000 GHz ( +- 0.10% )
0.002942516 seconds time elapsed ( +- 0.36% )
4,300,400 instructions # 0.97 insns per cycle ( +- 0.02% )
4,439,363 cycles # 0.000 GHz ( +- 0.08% )
0.002962733 seconds time elapsed ( +- 0.32% )
# Patched (x86_64-mem*.patch):
Performance counter stats for 'perf bench mem memcpy -r x86-64-unrolled' (1000 runs):
5,236,674 instructions # 1.01 insns per cycle ( +- 0.01% )
5,182,292 cycles # 0.000 GHz ( +- 0.07% )
0.003426389 seconds time elapsed ( +- 0.29% )
5,235,704 instructions # 1.01 insns per cycle ( +- 0.01% )
5,183,586 cycles # 0.000 GHz ( +- 0.08% )
0.003414827 seconds time elapsed ( +- 0.31% )
5,236,240 instructions # 1.01 insns per cycle ( +- 0.01% )
5,192,932 cycles # 0.000 GHz ( +- 0.10% )
0.003404885 seconds time elapsed ( +- 0.33% )
Performance counter stats for 'perf bench mem memset -r x86-64-unrolled' (1000 runs):
4,299,811 instructions # 0.97 insns per cycle ( +- 0.02% )
4,442,268 cycles # 0.000 GHz ( +- 0.09% )
0.002957321 seconds time elapsed ( +- 0.32% )
4,300,057 instructions # 0.97 insns per cycle ( +- 0.02% )
4,438,804 cycles # 0.000 GHz ( +- 0.09% )
0.002974749 seconds time elapsed ( +- 0.29% )
4,299,886 instructions # 0.97 insns per cycle ( +- 0.02% )
4,444,117 cycles # 0.000 GHz ( +- 0.11% )
0.002967353 seconds time elapsed ( +- 0.30% )
Jan
next prev parent reply other threads:[~2012-01-18 10:40 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-05 16:10 Jan Beulich
2012-01-06 11:05 ` Ingo Molnar
2012-01-06 12:31 ` Jan Beulich
2012-01-06 19:01 ` Ingo Molnar
2012-01-18 10:40 ` Jan Beulich [this message]
2012-01-18 11:14 ` Ingo Molnar
2012-01-18 13:33 ` Jan Beulich
2012-01-18 18:16 ` Linus Torvalds
2012-01-19 7:48 ` Jan Beulich
2012-01-19 12:18 ` Ingo Molnar
2012-01-26 13:40 ` [tip:x86/asm] x86-64: Fix " tip-bot for Jan Beulich
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