lkml.org 
[lkml]   [2004]   [Feb]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: 2.6.1 Scheduler Latency Measurements (Preemption diabled/enabled)
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/

\
 
 \ /
  Last update: 2005-03-22 14:01    [W:0.092 / U:0.084 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site