Messages in this thread | | | Date | Tue, 17 Feb 2004 22:41:30 -0500 | From | Bill Davidsen <> | Subject | Re: 2.6.1 Scheduler Latency Measurements (Preemption diabled/enabled) |
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Christoph Stueckjuergen wrote: > Hi, > > I performed a series of measurements comparing scheduler latency of a 2.6.1 > kernel with preemption enabled and disabled on an AMD Elan (i486 compatible) > with 133 Mhz clock frequency. > > The measurements were performed with a kernel module and a user mode process > that communicate via a character device interface. The user mode process uses > a blocking read() call to obtain data from the kernel. The kernel module > reads the system time every 10 ms by calling do_gettimeofday(), wakes up the > sleeping user mode process and passes the system time to it. After having > received the system time from the kernel, the user mode process reads the > system time by calling gettimeofday() and is thus able to determine the > scheduler latency by subtracting the two times. The user mode process is run > with the SCHED_FIFO scheduling policy. > > Measurements were carried out on a „loaded“ and an „unloaded“ system. The > „load“ was created by a process that continuously writes data to the serial > interface /dev/ttyS0. > > The results are: > "loaded" system, 10.000 samples > average scheduler latency (preemption enabled / disabled): 170 us / 232 us > minimum scheduler latency (preemption enabled / disabled): 49 us / 43 us > maximum scheduler latency (preemption enabled / disabled): 840 us / 1063 us > > "unloaded" system, 10.000 samples > average scheduler latency (preemption enabled / disabled): 50 us / 44 us > minimum scheduler latency (preemption enabled / disabled): 46 us / 41 us > maximum scheduler latency (preemption enabled / disabled): 233 us / 215 us > > Any help in interpreting the data would be highly appreciated. Especially: > - Why does preemption lead to a higher minimum scheduler latency in the loaded > case? > - Why does preemption worsen scheduler latency on the unloaded system? > > Best regards, > Christoph > > PS: I am not subscribed, please CC me if you answer!
Have you considered repeating your test on 2.6.3-rc3-mm1 or similar with all of the most recent thinking on scheduling?
-- bill davidsen <davidsen@tmr.com> CTO TMR Associates, Inc Doing interesting things with small computers since 1979 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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