Can we use CONFIG_PREEMPT to change lk 2.6 from preemptive kernel to lk 2.4-like non-preemptive one? If we can, how (which file should be modified and how) to do it? Thanks, T. --- Robert Love <rml@ximian.com> wrote: > On Thu, 2004-06-24 at 16:13 +0530, Dhiman, Gaurav > wrote: > > > You are right to great extent. As far as I > understand, in preemptive > > kernel the timer interrupt plays an important > role. On every > > timer-interrupt, it checks if the time allotted to > the current process > > is expired or not, in case it has not been expired > yet, it does not > > switch the current running task. If it finds that > the time allocated to > > current process has been expired, then it uses the > bottom half > > functionality of kernel to make the calls to > scheduler at some later > > time, when its bottom half handler will be called. > Scheduler will save > > the context of current running process (does not > matter if process is in > > user mode or in kernel mode, in both cases it will > switch). > > > > Frankly speaking this is my perception, it might > be wrong, if somebody > > finds it wrong, please correct it. > > Sure. > > A couple corrections: > > The timer interrupt does the timeslice check as you > describe in the same > manner, whether or not CONFIG_PREEMPT is enabled. > It simply sets the > need_resched flag. > > The actual preemption occurs when the timer > interrupt returns (it > actually occurs when any interrupt returns). If > need_resched is set, > the interrupt handler will invoke the scheduler to > choose a new task. > > With !CONFIG_PREEMPT, this can only occur if the > interrupt is returning > to user-space. > > With CONFIG_PREEMPT, this can additionally occur > when returning to > kernel-space if preempt_count==0. > > Bottom halves are not involved. > > Robert Love > > > > -- > Kernelnewbies: Help each other learn about the Linux > kernel. > Archive: > http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > > __________________________________ Do you Yahoo!? Yahoo! Mail - 50x more storage than other providers! http://promotions.yahoo.com/new_mail -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
