amd64/152405: wrong user time is reported when CPU frequency throttled.

[KOIE Hidetaka ( 鯉江英隆＠数理技研 )]

The following reply was made to PR amd64/152405; it has been noted by GNATS.

From: KOIE Hidetaka (=?iso-2022-jp?B?GyRCOHE5PjFRTjQhdz90TX01OzgmGyhC?=)
 <koie at suri.co.jp>
To: avg at freebsd.org
Cc: bug-followup at freebsd.org
Subject: Re: amd64/152405: wrong user time is reported when CPU frequency
 throttled.
Date: Thu, 25 Nov 2010 12:56:40 +0900 (JST)

   Message-Id: <4CED1EEC.5010107 at freebsd.org>
   Date:       Wed, 24 Nov 2010 16:19:24 +0200
   From:       Andriy Gapon <avg at freebsd.org>
   Subject:    Re: amd64/152405: wrong user time is reported when CPU f..
 
   | on 24/11/2010 15:54 Andriy Gapon said the following:
   | > Anyway, it seems that I missed the real cause of this problem and the excellent
   | > explanation by Bruce.
   | 
   | Could you please try the following (work-in-progress) patch?
   | http://people.freebsd.org/~avg/tsc-cpu_ticks.diff
 
 on the patched kernel, time command reports correct time!
 
     % sysctl kern.eventtimer.timer
     kern.eventtimer.timer: LAPIC
     % sudo sysctl dev.cpu.0.freq=1800
     Password:
     dev.cpu.0.freq: 1800 -> 1800
     % time ./loop
     ffffffff
     4.835u 0.007s 0:04.99 96.7%     5+2785k 0+0io 0pf+0w
     % sudo sysctl dev.cpu.0.freq=1000
     dev.cpu.0.freq: 1800 -> 1000
     % time ./loop
     ffffffff
     8.754u 0.000s 0:09.12 95.9%     5+2777k 0+0io 0pf+0w
     %
 
 Thank you.
 
   | 
   | I expect that it should improve accuracy for your testcase, but may penalize
   | system performance to certain degree.
   | 
   | As mav@ has said, performance, accuracy, powerstate management - pick any two of
   | the three.  OTOH, I am not sure by how much the performance could be affected.
 
 --
 KOIE Hidetaka