On Sat, Apr 29, 2006 at 17:08:38 +0530, Manjunath Naik wrote: > On 4/29/06, Hareesh Nagarajan <hnagar2@xxxxxxxxx> wrote: > >On 4/29/06, Manjunath Naik <peter.desouzain@xxxxxxxxx> wrote: > >> #define preempt_disable() \ > >> But I was not able to understand how exactly preempting works. when > > > >While we hold a spin lock to protect a critical region, it is > >necessary for us to disable preemption. To disable preemption, we > >increment the preempt count. > > > >> schedular wants to schedule the other process, it checks the > >> thread_info->preempt_count value? If it is yes plese provide me some > >links > >> or code reference for it. > > > >Documentation/preempt-locking.txt > > > If prempt_count is incremented how it will leads to disable the > preemption? who will check the counter? Is scheduler will check this counter > before selecting other process for context switch. If yes, how sheduler gets > the priority to run itself. The scheduler checks the preempt_count flag and will not preempt the running task if it's non-0. Scheduler is not a process. There are two entry points for it that are part of the interrupt handling code (so it gets a chance to run at least after each timer interrupt). One is during return to userspace (this was always there and handles preempting user-space code) and another along where bottom-halves are run, which deals with the preemption. -- Jan 'Bulb' Hudec <bulb@xxxxxx>
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