[Bug 70941] New: 'powersave' performance excessively slow on Dell Venue 8 Pro (Baytrail tablet)

[Bug 70941] New: 'powersave' performance excessively slow on Dell Venue 8 Pro (Baytrail tablet)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=70941

            Bug ID: 70941
           Summary: 'powersave' performance excessively slow on Dell Venue
                    8 Pro (Baytrail tablet)
           Product: Power Management
           Version: 2.5
    Kernel Version: 3.14rc3
          Hardware: i386
                OS: Linux
              Tree: Fedora
            Status: NEW
          Severity: high
          Priority: P1
         Component: cpufreq
          Assignee: cpufreq@vger.kernel.org
          Reporter: awilliam@redhat.com
        Regression: No

I've noticed recent 3.14 kernels perform extremely sluggishly on my Venue 8 Pro
(Baytrail-based tablet). Doing 'echo performance >
/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor' speeds things right up
again: default is 'powersave'.

Obviously performance will be faster, but powersave seems really egregiously
slow. Just stuff like paging through console output at a VT is incredibly
sluggish - I can run 'journalctl -b', hit End, and watch it draw one painful
line at a time.

The scaling_driver is 'intel_pstate' . I think pstate stuff may have been
broken on baytrail for a while - I had to boot with intel_pstate=disable for a
bit, and before that it may just not have been kicking in - which is probably
why I didn't notice this until rc2 or so.

The frequency range is 200MHz->1.6GHz with both 'powersave' and 'performance'.
I'm not sure what's the best way to watch the scaling kick in, but using
powertop or just spamming 'cat
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq' , it does seem to scale
up rather faster with performance.

Not sure what info is needed to help debug this, just ask and I'll provide.

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[Bug 70941] 'powersave' performance excessively slow on Dell Venue 8 Pro (Baytrail tablet)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=70941

Dirk Brandewie <dirk.brandewie@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dirk.brandewie@gmail.com

--- Comment #1 from Dirk Brandewie <dirk.brandewie@gmail.com> ---


commit fcb6a15c2e7e76d493e6f91ea889ab40e1c643a4 is the problem.  I am working
on a fix ATM.

Lowering the setpoint for the PID should workaround the problem

echo 90 > /sys/kernel/debug/pstate_snb/setpoint

This will cost some power though.

This also broke GregKH
https://lkml.org/lkml/2014/2/19/626

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[Bug 70941] 'powersave' performance excessively slow on Dell Venue 8 Pro (Baytrail tablet)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=70941

Lan Tianyu <tianyu.lan@intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|cpufreq@vger.kernel.org     |dirk.brandewie@gmail.com
             Status|NEW                         |ASSIGNED
                 CC|                            |tianyu.lan@intel.com

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