On 12/05/2013 01:26 PM, Daniil Lunev wrote:
508
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#508>/*
509
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#509>
* Given the old percent cpu and a time delta in nanoseconds,
510
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#510>
* return the new decayed percent cpu: pct * exp(-tau),
511
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#511>
* where 'tau' is the time delta multiplied by a decay factor.
512 <http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#512>
* We have chosen the decay factor (cpu_decay_factor inparam.c
<http://src.illumos.org/source/s?path=param.c&project=illumos-gate>)
513
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#513>
* to make the decay over five seconds be approximately 20%.
514
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#514>
*
515
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#515>
* 'pct' is a 32-bit scaled integer <= 1
516
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#516>
* The binary point is to the right of the high-order bit
517
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#517>
* of the 32-bit word.
518
<http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/os/msacct.c#518>
*/
According to the commentary t_pctcpu seems not to be very precise.
For most purposes I found, t_pctcpu is sufficient. But I'd suggest
trying it out and seeing if it fits what you need instead of relying on
the comment.
Maybe I missed this from an earlier email, but we would be able to
provide more guidance if we knew what you're trying to accomplish.
But even with this param we haven't a mechanism for estimating, say,
"cpu usage" of the functions (mean, what part of the cpu usage a
function takes), except dtrace that can not be used from the kernel.
--Daniil Lunev
Per function metrics such as what you're describing are not something
one should expect a general purpose OS to provide by default. If you're
looking at time deltas between states or events, micro-state accounting
might help you. If you're doing source analysis, then DTrace is likely
what you're looking for.
Rafael
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