From: Erik Slagter <erik@slagter.name>
To: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
Cc: cpufreq@www.linux.org.uk
Subject: Re: [PATCH] acpi-cpufreq: Use IA32_APERF and IA32_MPERF and get freq feedback from hardware
Date: Mon, 25 Sep 2006 21:07:15 +0200 [thread overview]
Message-ID: <451828E3.6040607@slagter.name> (raw)
In-Reply-To: <EB12A50964762B4D8111D55B764A8454A41225@scsmsx413.amr.corp.intel.com>
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Pallipadi, Venkatesh wrote:
> You can look at /sys/..../cpufreq/cpuinfo_cur_freq to get the
> instantaneous frequency from hardware (But only works when MSR based
> transitions are used. There is no way to get current frequency when IO
> port based transitions are being used).
> /sys/..../cpufreq/scaling_cur_freq and /proc/cpuinfo shows the last
> value that cpufreq tried to set.
These only give the frequencies the CPU was "designed" for, not the
actual frequency. Only the information in /proc/cpuinfo is correct, at
least, until cpufreq comes in.
> I am not sure how ondemand can help with more performance with C1E. One
> possible explanation:
> With C1E, hardware goes to lower frequency on idle by itself. Only
> difference ondemand can be making is running at a lower frequency even
> when CPU is busy and average utilization is low. Due to this CPU can run
> cooler than without ondemand. And due to that TM2 may not kick in as
> frequently as it would without the ondemand. But, I am not sure how C1E
> makes the difference here. This behavior should be same with ot without
> C1E capable CPU. What is the workload you have. Partially idle? What is
> the CPU utilization over time?
I observe this while compiling the kernel. It shows a consistent
discrepancy of a few seconds on a total of ~2:45 compile time. I am not
complaining ;-)
Is there a way to know for shure if either tm1 or tm2 kicked in? I'd
really like to know, I want to have max performance. If tm? kicks in, I
won't get that of course. If I know if/when it happens, I can try a
lower frequency or better cooling.
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next prev parent reply other threads:[~2006-09-25 19:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-25 16:36 [PATCH] acpi-cpufreq: Use IA32_APERF and IA32_MPERF and get freq feedback from hardware Pallipadi, Venkatesh
2006-09-25 19:07 ` Erik Slagter [this message]
2006-10-02 23:03 ` Dominik Brodowski
-- strict thread matches above, loose matches on Subject: below --
2006-09-25 14:41 Pallipadi, Venkatesh
2006-09-25 16:02 ` Erik Slagter
2006-09-23 0:28 Venkatesh Pallipadi
2006-09-25 13:14 ` Erik Slagter
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