1. 19 Dec, 2018 1 commit
    • Vincent Guittot's avatar
      PM-runtime: Switch autosuspend over to using hrtimers · 8234f673
      Vincent Guittot authored
      PM-runtime uses the timer infrastructure for autosuspend. This implies
      that the minimum time before autosuspending a device is in the range
      of 1 tick included to 2 ticks excluded
       -On arm64 this means between 4ms and 8ms with default jiffies
        configuration
       -And on arm, it is between 10ms and 20ms
      
      These values are quite high for embedded systems which sometimes want
      the duration to be in the range of 1 ms.
      
      It is possible to switch autosuspend over to using hrtimers to get
      finer granularity for short durations and take advantage of slack to
      retain some margins and get long timeouts with minimum wakeups.
      
      On an arm64 platform that uses 1ms for autosuspending timeout of its
      GPU, idle power is reduced by 10% with hrtimer.
      
      The latency impact on arm64 hikey octo cores is:
       - mark_last_busy: from 1.11 us to 1.25 us
       - rpm_suspend: from 15.54 us to 15.38 us
      [Only the code path of rpm_suspend() that starts hrtimer has been
      measured.]
      
      arm64 image (arm64 default defconfig) decreases by around 3KB
      with following details:
      
      $ size vmlinux-timer
         text	   data	    bss	    dec	    hex	filename
      12034646	6869268	 386840	19290754	1265a82	vmlinux
      
      $ size vmlinux-hrtimer
         text	   data	    bss	    dec	    hex	filename
      12030550	6870164	 387032	19287746	1264ec2	vmlinux
      
      The latency impact on arm 32bits snowball dual cores is :
       - mark_last_busy: from 0.31 us usec to 0.77 us
       - rpm_suspend: from 6.83 us to 6.67 usec
      
      The increase of the image for snowball platform that I used for
      testing performance impact, is neglictable (244B).
      
      $ size vmlinux-timer
         text	   data	    bss	    dec	    hex	filename
      7157961	2119580	 264120	9541661	 91981d	build-ux500/vmlinux
      
      size vmlinux-hrtimer
         text	   data	    bss	    dec	    hex	filename
      7157773	21198846	 264248	9541905	 919911	vmlinux-hrtimer
      
      And arm 32bits image (multi_v7_defconfig) increases by around 1.7KB
      with following details:
      
      $ size vmlinux-timer
         text	   data	    bss	    dec	    hex	filename
      13304443	6803420	 402768	20510631	138f7a7	vmlinux
      
      $ size vmlinux-hrtimer
         text	   data	    bss	    dec	    hex	filename
      13304299	6805276	 402768	20512343	138fe57	vmlinux
      Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
      Reviewed-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
      Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
      8234f673
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