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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-05-04 14:01:10 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-05-04 14:09:16 +0200
commit6d45b719cbd51f014bb1b5dd8ed99068d78d36af (patch)
treec49822a308038696cbea7e1ea466a6b3248b1efd /drivers/base
parentba41e1bc28bd862089b0fc00e8136aa258a62b21 (diff)
downloadop-kernel-dev-6d45b719cbd51f014bb1b5dd8ed99068d78d36af.zip
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intel_pstate: Fix intel_pstate_get()
After commit 8fa520af5081 "intel_pstate: Remove freq calculation from intel_pstate_calc_busy()" intel_pstate_get() calls get_avg_frequency() to compute the average frequency, which is problematic for two reasons. First, intel_pstate_get() may be invoked before the driver reads the CPU feedback registers for the first time and if that happens, get_avg_frequency() will attempt to divide by zero. Second, the get_avg_frequency() call in intel_pstate_get() is racy with respect to intel_pstate_sample() and it may end up returning completely meaningless values for this reason. Moreover, after commit 7349ec0470b6 "intel_pstate: Move intel_pstate_calc_busy() into get_target_pstate_use_performance()" sample.core_pct_busy is never computed on Atom, but it is used in intel_pstate_adjust_busy_pstate() in that case too. To address those problems notice that if sample.core_pct_busy was used in the average frequency computation carried out by get_avg_frequency(), both the divide by zero problem and the race with respect to intel_pstate_sample() would be avoided. Accordingly, move the invocation of intel_pstate_calc_busy() from get_target_pstate_use_performance() to intel_pstate_update_util(), which also will take care of the uninitialized sample.core_pct_busy on Atom, and modify get_avg_frequency() to use sample.core_pct_busy as per the above. Reported-by: kernel test robot <ying.huang@linux.intel.com> Link: http://marc.info/?l=linux-kernel&m=146226437623173&w=4 Fixes: 8fa520af5081 "intel_pstate: Remove freq calculation from intel_pstate_calc_busy()" Fixes: 7349ec0470b6 "intel_pstate: Move intel_pstate_calc_busy() into get_target_pstate_use_performance()" Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/base')
0 files changed, 0 insertions, 0 deletions
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