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    <title>Intel Software Network Comments Feed</title>
    <link>http://software.intel.com/en-us/articles/best-timing-function-for-measuring-ipp-api-timing</link>
    <description></description>
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    <item>
      <title>By A. Boyer</title>
      <description><![CDATA[ Other Intel sources indicate that the TSC is shared between cores, but not synchronized among multiple physical CPUs.  Otherwise, what is the point of the RDTSCP instruction? ]]></description>
      <link>http://software.intel.com/en-us/articles/best-timing-function-for-measuring-ipp-api-timing/#comment-41482</link>
      <pubDate>Mon, 29 Mar 2010 08:06:34 -0700</pubDate>
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      <title>By Vipin Kumar E K (Intel)</title>
      <description><![CDATA[ For the latest Nehalem processors, the time stamp counter (RDTSC) does not vary with the actual operating frequency of the part. This is referred to as "Invariant TSC" and described in the software developers manual (SDM) section 16.11.1 ( http://www.intel.com/Assets/PDF/manual/253668.pdf ). 

Unlike prior parts, Nehalem's TSC does not stop across core C-states. Nehalem also implements the RDTSCP instruction which returns both the TSC value and a new MSR into ECX. For a full explanation of RDTSCP, please see the SDM.

On Nehalem, the TSC runs at a constant frequency of MSR_PLATFORM_INFO[15:8] * 133.33MHz. MSR_PLATFORM_INFO[15:8] will report the lower of the ratio at which the part was stamped or a separate MSR to lower the ratio to provide TSC consistency across multi-socket systems with parts of different frequencies.

Synchronization of the TSC across multiple threads/cores/packages:  As long as software does not write the TSC, the Nehalem TSC will remain synchronized across all threads, cores and packages connected to a single PCH.

The time-stamp counter on Nehalem is reset to zero each time the processor package has RESET asserted. From that point onwards the TSC will continue to tick constantly across frequency changes, turbo mode and ACPI C-states. All parts that see RESET synchronously will have their TSC's completely synchronized. This synchronous distribution of RESET is required for all sockets connected to a single PCH. For large, multi-node systems, RESET might not be synchronous.


--Vipin ]]></description>
      <link>http://software.intel.com/en-us/articles/best-timing-function-for-measuring-ipp-api-timing/#comment-42110</link>
      <pubDate>Mon, 12 Apr 2010 02:52:55 -0700</pubDate>
      <guid isPermaLink="true">http://software.intel.com/en-us/articles/best-timing-function-for-measuring-ipp-api-timing/#comment-42110</guid>
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    <item>
      <title>By Matt</title>
      <description><![CDATA[ 
Okay... so I have the execution time in clocks.  How do I convert that reliably to ms?

Thanks.
 ]]></description>
      <link>http://software.intel.com/en-us/articles/best-timing-function-for-measuring-ipp-api-timing/#comment-42548</link>
      <pubDate>Fri, 23 Apr 2010 07:16:44 -0700</pubDate>
      <guid isPermaLink="true">http://software.intel.com/en-us/articles/best-timing-function-for-measuring-ipp-api-timing/#comment-42548</guid>
    </item>
    <item>
      <title>By caddie</title>
      <description><![CDATA[ I think the answer is in Vipin's post Matt. You've got the TSC, which ticks at a constant rate, so you can divide the counter with that constant. Please read Vipin's post carefully. ]]></description>
      <link>http://software.intel.com/en-us/articles/best-timing-function-for-measuring-ipp-api-timing/#comment-61002</link>
      <pubDate>Thu, 23 Jun 2011 17:43:09 -0700</pubDate>
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