[Xen-bugs] [Bug 108] Xen domain scheduler allows only 50% physical cpu usage

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=108





------- Additional Comments From habanero@xxxxxxxxxx  2005-08-18 15:47 -------
OK, we seem to have a problem with time keeping on x86_64.  I noticed this when
most benchmarks on Xen get less than 1/2 the throughput than native Linux,
however all the reaim benchmarks did not.  The reaim benchmarks probably compute
time differently.  So, to make sure we had a trusted wall clock time reference,
I ran dbench but ssh'd for 'date' to another system before and after.  The
benchmark harness also reported local call to date:

               "ssh host date"                local date
              before    after                before    after
native Linux: 09:57:33  10:09:41 ~12 mins  00:00:13  00:12:18 ~12 mins
xen0 Linux:   10:18:14  10:24:22  ~6 mins  00:20:54  00:27:00  ~6 mins

So, wall clock timeis OK, but the xen0 dbench runs ran in 1/2 the expected 
time.  
Additionally, dbench reports elapsed time as it runs, and both runs looked like:

Running for 600 seconds with load '/autobench/sources/dbench3/client.txt'
  and ms16 clients started
  16      4761   513.24 MB/sec  warmup   1 sec
  16     11169   533.08 MB/sec  warmup   2 sec
  16     16500   534.30 MB/sec  warmup   3 sec
  16     21903   532.74 MB/sec  warmup   4 sec
  16     28053   532.70 MB/sec  warmup   5 sec
 <snip>
  16    671009   498.23 MB/sec  warmup 117 sec
  16    677205   498.55 MB/sec  warmup 118 sec
  16    683536   498.90 MB/sec  warmup 119 sec
  16    695893   554.03 MB/sec  execute   1 sec
  16    702155   542.27 MB/sec  execute   2 sec
  16    708169   536.73 MB/sec  execute   3 sec
<snip>
  16   4090403   492.85 MB/sec  execute 599 sec
  16   4096510   492.90 MB/sec  cleanup 600 sec
  16   4096510   492.08 MB/sec  cleanup 601 sec
  16   4096510   491.28 MB/sec  cleanup 602 sec

So, both dbench runs report running for 12 minutes total, but xen0 run really
ran for 6.  It sounds like domain virtual time is running at a rate 2x of wall
clock time.




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