Messages in this thread | | | Date | Thu, 22 Mar 2007 05:18:17 -0700 | From | Venkatesh Pallipadi <> | Subject | Re: [PATCH 1/2] Add support for deferrable timers |
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On Thu, Mar 22, 2007 at 03:18:26AM -0800, Andrew Morton wrote: > On Wed, 21 Mar 2007 13:22:17 -0700 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> wrote: > > > > > Introduce a new flag for timers - 'deferrable timer' > > Timers that work normally when system is busy. But, will not cause CPU to > > come out of idle (just to service this timer), when CPU is idle. Instead, > > this timer will be serviced when CPU eventually wakes up with a subsequent > > non-deferrable timer or any other event. > > > > The main advantage of this is to avoid unnecessary timer interrupts when > > CPU is idle. If the routine currently called by a timer can wait until next > > event without any issues, this new timer can be used while setting up timer > > for that routine. This, with dynticks, allows CPUs to be lazy, allowing them > > to stay in idle for extended period of time by reducing unnecesary wakeup and > > thereby reducing the power consumption. > > > > This patch: > > Builds this new timer on top of existing timer infrastructure. It uses > > last bit in 'base' pointer of timer_list structure to store this > > deferrable timer flag. __next_timer_interrupt() function > > skips over these deferrable timers when CPU looks for > > next timer event for which it has to wake up. > > > > This is exported by a new interface init_timer_deferrable() that can > > be called in place of regular init_timer(). > > > > These patches cause a lockup during execuion of `halt -p'. See phuzzy foto > at http://userweb.kernel.org/~akpm/s5000486.jpg > > It's fairly obvious why, when one looks at lock_timer_base().
Hmm.. Wonder how it worked for me and why I did not see this hang. I had thought I covered all accesses to ->base. Obviously, I have missed this "base == timer->base" check here. Will fix it and respin a patch later today with below suggestions as well.
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