Re: [rcu] 7c66b15f870: +1.8% turbostat.Pkg_W

[Fengguang Wu <fengguang.wu@intel.com>]

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On Wed, Jun 25, 2014 at 07:10:23PM -0700, Paul E. McKenney wrote:
> On Thu, Jun 26, 2014 at 09:33:08AM +0800, Fengguang Wu wrote:
> > Hi Paul,
> > 
> > We noticed increased power consumption in our internal merge commit.
> > It's not a direct evidence, however in the hope you can see any
> > obvious clues. :)
> 
> Hello, Fengguang,
> 
> This particular branch is obsolete, and has been replaced by commit
> 4a81e8328d37 (Reduce overhead of cond_resched() checks for RCU).

Ah great, we happen to have more direct numbers for that patch. :)

> Just out of curiosity, how do you measure the power consumption?

It's read by the turbostat tool, from CPU MSRs:

commit 889facbee3e67dbc8eb29d8ee7fd66d33a647bfc
Author:     Len Brown <len.brown@intel.com>
AuthorDate: Thu Nov 8 00:48:57 2012 -0500
Commit:     Len Brown <len.brown@intel.com>
CommitDate: Fri Nov 30 01:09:44 2012 -0500

    tools/power turbostat: v3.0: monitor Watts and Temperature

    Show power in Watts and temperature in Celsius
    when hardware support is present.

    Intel's Sandy Bridge and Ivy Bridge processor generations support RAPL
    (Run-Time-Average-Power-Limiting).  Per the Intel SDM
    (Intel® 64 and IA-32 Architectures Software Developer Manual)
    RAPL provides hardware energy counters and power control MSRs
    (Model Specific Registers).  RAPL MSRs are designed primarily
    as a method to implement power capping.  However, they are useful
    for monitoring system power whether or not power capping is used.

    In addition, Turbostat now shows temperature from DTS
    (Digital Thermal Sensor) and PTM (Package Thermal Monitor) hardware,
    if present.

    As before, turbostat reads MSRs, and never writes MSRs.

    New columns are present in turbostat output:

    The Pkg_W column shows Watts for each package (socket) in the system.
    On multi-socket systems, the system summary on the 1st row shows the sum
    for all sockets together.

    The Cor_W column shows Watts due to processors cores.
    Note that Core_W is included in Pkg_W.

    The optional GFX_W column shows Watts due to the graphics "un-core".
    Note that GFX_W is included in Pkg_W.

    The optional RAM_W column on server processors shows Watts due to DRAM DIMMS.
    As DRAM DIMMs are outside the processor package, RAM_W is not included in Pkg_W.

    The optional PKG_% and RAM_% columns on server processors shows the % of time
    in the measurement interval that RAPL power limiting is in effect on the
    package and on DRAM.

    Note that the RAPL energy counters have some limitations.

    First, hardware updates the counters about once every milli-second.
    This is fine for typical turbostat measurement intervals > 1 sec.
    However, when turbostat is used to measure events that approach
    1ms, the counters are less useful.

    Second, the 32-bit energy counters are subject to wrapping.
    For example, a counter incrementing 15 micro-Joule units
    on a 130 Watt TDP server processor could (in theory)
    roll over in about 9 minutes.  Turbostat detects and handles
    up to 1 counter overflow per measurement interval.
    But when the measurement interval exceeds the guaranteed
    counter range, we can't detect if more than 1 overflow occured.
    So in this case turbostat indicates that the results are
    in question by replacing the fractional part of the Watts
    in the output with "**":

    Pkg_W  Cor_W GFX_W
      3**    0**   0**

    Third, the RAPL counters are energy (Joule) counters -- they sum up
    weighted events in the package to estimate energy consumed.  They are
    not analong power (Watt) meters.  In practice, they tend to under-count
    because they don't cover every possible use of energy in the package.
    The accuracy of the RAPL counters will vary between product generations,
    and between SKU's in the same product generation, and with temperature.

    turbostat's -v (verbose) option now displays more power and thermal configuration
    information -- as shown on the turbostat.8 manual page.
    For example, it now displays the Package and DRAM Thermal Design Power (TDP):

    cpu0: MSR_PKG_POWER_INFO: 0x2f064001980410 (130 W TDP, RAPL 51 - 200 W, 0.045898 sec.)
    cpu0: MSR_DRAM_POWER_INFO,: 0x28025800780118 (35 W TDP, RAPL 15 - 75 W, 0.039062 sec.)
    cpu8: MSR_PKG_POWER_INFO: 0x2f064001980410 (130 W TDP, RAPL 51 - 200 W, 0.045898 sec.)
    cpu8: MSR_DRAM_POWER_INFO,: 0x28025800780118 (35 W TDP, RAPL 15 - 75 W, 0.039062 sec.)

    Signed-off-by: Len Brown <len.brown@intel.com>
---
 tools/power/x86/turbostat/turbostat.8 | 103 ++++--
 tools/power/x86/turbostat/turbostat.c | 643 ++++++++++++++++++++++++++++++++--
 2 files changed, 690 insertions(+), 56 deletions(-)