Freely quoting from boinc_alpha list
SekeRob
Seen several times on the WCG member forums there was the assertion that
the particular rule after 6.2.28 is to 'only' use the & of processors. I
did test percent of processors on my Octo, in Windows 7-64, and 87.5 did
drop the running threads to 7,

18/06/2013 19:29:57 |  | Number of usable CPUs has changed from 8 to 7.
18/06/2013 19:29:57 |  | max CPUs used: 7
18/06/2013 19:29:57 |  | don't use GPU while active
18/06/2013 19:29:57 |  | suspend work if non-BOINC CPU load exceeds 75 %
18/06/2013 19:29:57 |  | (to change preferences, visit a project web
site or select Preferences in the Manager)
18/06/2013 19:29:58 | World Community Grid | [cpu_sched] Preempting
DSFL_00090-45_0000011_0446_4 (left in memory)

  even 25% dropped it to just 2.

18/06/2013 19:31:04 |  | Number of usable CPUs has changed from 7 to 2.
18/06/2013 19:31:04 |  | max CPUs used: 2
18/06/2013 19:31:04 |  | don't use GPU while active
18/06/2013 19:31:04 |  | suspend work if non-BOINC CPU load exceeds 75 %
18/06/2013 19:31:04 |  | (to change preferences, visit a project web
site or select Preferences in the Manager)
18/06/2013 19:31:04 | World Community Grid | [cpu_sched] Preempting
DSFL_00090-35_0000018_0355_0 (left in memory)
18/06/2013 19:31:04 | World Community Grid | [cpu_sched] Preempting
DSFL_00090-35_0000017_0097_0 (left in memory)
18/06/2013 19:31:04 | World Community Grid | [cpu_sched] Preempting
DSFL_00090-35_0000017_0044_0 (left in memory)
18/06/2013 19:31:04 | World Community Grid | [cpu_sched] Preempting
DSFL_00090-35_0000018_0741_0 (left in memory)
18/06/2013 19:31:04 | World Community Grid | [cpu_sched] Preempting
DSFL_00090-35_0000018_0555_0 (left in memory)

Alternating here due the coming and going heat. Since presently testing
the WCG build 7.0.68 [the DCF fix applied, as properties no longer shows
it on this project, but on others without the <dont_use_dcf/> do in the
BM], tried it just now, with the said 25% in local prefs and 2
processors on website, leaving the % there at 100%. Updated, and then
increased local pref to 37.5%.

18/06/2013 19:32:42 |  | max CPUs used: 2
18/06/2013 19:32:42 |  | don't use GPU while active
18/06/2013 19:32:42 |  | suspend work if non-BOINC CPU load exceeds 75 %
18/06/2013 19:32:42 |  | (to change preferences, visit a project web
site or select Preferences in the Manager)
18/06/2013 19:32:42 | World Community Grid | [sched_op] Deferring
communication for 21 sec
18/06/2013 19:32:42 | World Community Grid | [sched_op] Reason:
requested by project
18/06/2013 19:33:24 | World Community Grid | General prefs: from World
Community Grid (last modified 18-Jun-2013 19:32:29)
18/06/2013 19:33:24 | World Community Grid | Host location: none
18/06/2013 19:33:24 | World Community Grid | General prefs: using your
defaults
18/06/2013 19:33:24 |  | Reading preferences override file
18/06/2013 19:33:24 |  | Preferences:
18/06/2013 19:33:24 |  | max memory usage when active: 6918.88MB
18/06/2013 19:33:24 |  | max memory usage when idle: 7732.87MB
18/06/2013 19:33:24 |  | max disk usage: 5.00GB
18/06/2013 19:33:24 |  | Number of usable CPUs has changed from 2 to 3.
18/06/2013 19:33:24 |  | max CPUs used: 3
18/06/2013 19:33:24 |  | don't use GPU while active
18/06/2013 19:33:24 |  | suspend work if non-BOINC CPU load exceeds 75 %
18/06/2013 19:33:24 |  | (to change preferences, visit a project web
site or select Preferences in the Manager)
18/06/2013 19:33:25 | World Community Grid | [cpu_sched] Resuming
DSFL_00090-35_0000018_0355_0
18/06/2013 19:33:25 | World Community Grid | Resuming task
DSFL_00090-35_0000018_0355_0 using dsfl version 625 in slot 0

Seems here things work as per expected... the % overrides the processors
hard number from website location aka global_preferences. Finally set
local prefs to 87.5% and then to 100%, and log response is still
following correctly.

18/06/2013 19:37:29 | World Community Grid | General prefs: from World
Community Grid (last modified 18-Jun-2013 19:32:29)
18/06/2013 19:37:29 | World Community Grid | Host location: none
18/06/2013 19:37:29 | World Community Grid | General prefs: using your
defaults
18/06/2013 19:37:29 |  | Reading preferences override file
18/06/2013 19:37:29 |  | Preferences:
18/06/2013 19:37:29 |  | max memory usage when active: 6918.88MB
18/06/2013 19:37:29 |  | max memory usage when idle: 7732.87MB
18/06/2013 19:37:29 |  | max disk usage: 5.00GB
18/06/2013 19:37:29 |  | Number of usable CPUs has changed from 3 to 7.
18/06/2013 19:37:29 |  | max CPUs used: 7
18/06/2013 19:37:29 |  | don't use GPU while active
18/06/2013 19:37:29 |  | suspend work if non-BOINC CPU load exceeds 75 %
18/06/2013 19:37:29 |  | (to change preferences, visit a project web
site or select Preferences in the Manager)
18/06/2013 19:37:29 | World Community Grid | [cpu_sched] Resuming
DSFL_00090-35_0000017_0097_0
18/06/2013 19:37:29 | World Community Grid | Resuming task
DSFL_00090-35_0000017_0097_0 using dsfl version 625 in slot 2
18/06/2013 19:37:29 | World Community Grid | [cpu_sched] Resuming
DSFL_00090-35_0000017_0044_0
18/06/2013 19:37:29 | World Community Grid | Resuming task
DSFL_00090-35_0000017_0044_0 using dsfl version 625 in slot 7
18/06/2013 19:37:29 | World Community Grid | [cpu_sched] Resuming
DSFL_00090-35_0000018_0741_0
18/06/2013 19:37:29 | World Community Grid | Resuming task
DSFL_00090-35_0000018_0741_0 using dsfl version 625 in slot 6
18/06/2013 19:37:29 | World Community Grid | [cpu_sched] Resuming
DSFL_00090-35_0000018_0555_0
18/06/2013 19:37:29 | World Community Grid | Resuming task
DSFL_00090-35_0000018_0555_0 using dsfl version 625 in slot 3
18/06/2013 19:37:45 | World Community Grid | General prefs: from World
Community Grid (last modified 18-Jun-2013 19:32:29)
18/06/2013 19:37:45 | World Community Grid | Host location: none
18/06/2013 19:37:45 | World Community Grid | General prefs: using your
defaults
18/06/2013 19:37:45 |  | Reading preferences override file
18/06/2013 19:37:45 |  | Preferences:
18/06/2013 19:37:45 |  | max memory usage when active: 6918.88MB
18/06/2013 19:37:45 |  | max memory usage when idle: 7732.87MB
18/06/2013 19:37:45 |  | max disk usage: 5.00GB
18/06/2013 19:37:45 |  | Number of usable CPUs has changed from 7 to 8.
18/06/2013 19:37:45 |  | don't use GPU while active
18/06/2013 19:37:45 |  | suspend work if non-BOINC CPU load exceeds 75 %
18/06/2013 19:37:45 |  | (to change preferences, visit a project web
site or select Preferences in the Manager)
18/06/2013 19:37:46 | World Community Grid | [cpu_sched] Resuming
DSFL_00090-35_0000018_0750_0
18/06/2013 19:37:46 | World Community Grid | Resuming task
DSFL_00090-35_0000018_0750_0 using dsfl version 625 in slot 4

Any other test that's missed to replicate the fail?

-- SekeRob