linux-kernel - Re: [RFC PATCH] crypto: crc32c-pclmul

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Date:	Fri, 30 May 2014 10:56:32 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Dave Jones <davej@...hat.com>,
	"dirk.brandewie@...il.com" <dirk.brandewie@...il.com>
Cc:	George Spelvin <linux@...izon.com>, herbert@...dor.apana.org.au,
	james.guilford@...el.com, JBeulich@...e.com,
	linux-kernel@...r.kernel.org,
	Jacob jun Pan <jacob.jun.pan@...el.com>
Subject: Re: [RFC PATCH] crypto: crc32c-pclmul - Use pmovzxdq to shrink
 K_table

On Thu, 2014-05-29 at 21:16 -0400, Dave Jones wrote:
> On Thu, May 29, 2014 at 06:07:16PM -0700, Tim Chen wrote:
>  > On Thu, 2014-05-29 at 19:54 -0400, George Spelvin wrote:
>  > > Sorry for the delay; my Ivy Bridge test machine isn't in my
>  > > office and getting to the console to tweak the BIOS is a
>  > > bit of a bother.
>  > > 
>  > > Anyway, i7-4930K, turbo boost & hyperthreading disabled,
>  > > $ cat /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor
>  > > performance
>  > > performance
>  > > performance
>  > > performance
>  > > performance
>  > > performance
>  > > 
>  > > Oddly, though, CPU speed still seems to be fluctuating:
>  > > $ grep MHz /proc/cpuinfo
>  > > cpu MHz         : 1255.875
>  > > cpu MHz         : 3168.375
>  > > cpu MHz         : 3062.125
>  > > cpu MHz         : 1468.375
>  > > cpu MHz         : 1309.000
>  > > cpu MHz         : 2212.125
>  > > $ grep MHz /proc/cpuinfo
>  > > cpu MHz         : 1255.875
>  > > cpu MHz         : 2690.250
>  > > cpu MHz         : 1255.875
>  > > cpu MHz         : 2530.875
>  > > cpu MHz         : 2212.125
>  > > cpu MHz         : 1521.500
>  > 
>  > This is odd.  On my Ivy Bridge system the CPU speed from /proc/cpuinfo 
>  > is at max freq once I set the performance governor.  
>  > The numbers above almost look like
>  > the cpu frequency is fluctuating and an average is taken.
>  > What version of the kernel are you running?  Is 
>  > CONFIG_CPU_FREQ_GOV_PERFORMANCE compiled in?
>  > 
>  > Does /sys/devices/system/cpu/cpu?/cpufreq/scaling_cur_freq
>  > also changes?
>  > 
>  > Can you check what are the available governors in your system
>  > and available frequencies?
>  > 
>  > cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
>  > cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
>  > 
>  > If userspace governor is available, you can try set the governor
>  > to userspace, then pin frequency to 3400 MHz (assuming that's your
>  > max) with command like:
>  
> intel_pstate overrides any governor choice you make through sysfs.
> 
> 	Dave
> 

Dirk,

Wonder if this the right behavior for intel_pstate that when I set the 
governor to performance, intel_pstate driver still adjusts 
the cpu frequencies around?

Turbotstat also confirms that the frequencies are not at max,
even though the max_perf_pct and min_perf_pct are both set at 100.  

I ran on my HSW system with 3.15-rc7 kernel and see similar
issue that Geroge reported.

It is really a pain when we need to do performance benchmarking and 
need to have a constant cpu frequency.  

Thanks.

Tim

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