On Tue, Aug 17, 2010 at 12:45 PM, Nivedita Singhvi <niv@xxxxxxxxxx> wrote: > On 08/17/2010 11:24 AM, Manikandan Ramachandran wrote: > >> Thanks David& Mark for your valuable input! >> >> I'm not expecting RT kernel to be real fast. However I expect latency >> of higher priority task to be less in RT kernel. I'll run the tests >> that you have suggested and see if there is any inherent issue with my >> system. > > Actually, a more accurate statement would be "I expect max latency > of higher priority task to be less in RT kernel." > > This is true for max latency as reported by you (max, min): > > Stock: 418011us 3s > RT: 366156us 3s > > So while the min might reflect the best that the system can do, the > max does seem a tad high -- you do need to look into that. > >> One more query, with RT patch is it possible for higher priority task >> to preempt a lower priority IRQ thread [For eg, IDE] ? If so when does >> that happen, during next timer interrupt [Assuming IRQ thread uses >> whole schedule slot and doesn't yield between]? > > Yes, and when that higher priority task becomes runnable. > > thanks, > Nivedita > -- I see a scenario where higher priority task is ready to run but lower priority IRQ thread is hogging the cpu. Please see the timeline log below: GIVE ffff0c1c [Comment: High priority IRQ thread wakes up high priority process at jiffy 0xffff0c1c] **ffff0c21**##ffff0c21##**ffff0c21**##ffff0c21##**ffff0c21**##ffff0c21##**ffff0c21**##ffff0c21##**ffff0c21**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c23**##ffff0c23##**ffff0c23**##ffff0c23##**ffff0c23**##ffff0c24##**ffff0c24**##ffff0c24##**ffff0c24**##ffff0c24## [Comment: Low priority IDE[ide_intr] handler hogs CPU for almost 3 ms] GOTffff0c26 [Comment: High priority task wakes up after 10 ms!!] I fail to understand why scheduler failed to schedule high priority task 10 times in a row. FYI, I have put IDE thread to SCHED_NORMAL while high priority thread and task to SCHED_FIFO. -- Thanks, Manik -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
