Messages in this thread | | | Date | Tue, 13 Sep 2011 15:06:58 -0500 | From | Shawn Bohrer <> | Subject | Re: [PATCH] sched_rt: Migrate equal priority tasks to available CPUs |
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On Tue, Sep 13, 2011 at 11:27:14AM -0500, Shawn Bohrer wrote: > On Tue, Sep 13, 2011 at 09:05:46AM -0400, Steven Rostedt wrote: > > Looks good, but do you have a test case that shows the issue? I like to > > have something that proves even the obvious before making changes to the > > schedule. > > I played around a little this morning trying to make a simple test case > that reproduces the issue, but so far I've been unsuccessful. My simple > test cases trying to simulate the workload above actually do get evenly > distributed across all CPUs. If I get some more time I'll see if I can > get an example to trigger the issue, but feel free to see if you can > reproduce it as well.
Alright, I'm still having trouble making a case that actually resulted in some CPUs left completely idle while others are loaded, but the rough test case below does still show the benefit of the patch.
$ gcc -o sched_rt_migration sched_rt_migration.c $ chrt -f 1 ./sched_rt_migration &
# Run 5 times with 3.0 $ sudo trace-cmd record -e sched:sched_switch -e sched:sched_wakeup sleep 1 $ trace-cmd report -r -w -F 'sched: comm == "sched_rt_migrat" || next_comm == "sched_rt_migrat"' | tail -4
Wakeup Latency Average: 2.551 usecs Max: 188.409 usecs Average: 2.372 usecs Max: 187.185 usecs Average: 2.559 usecs Max: 182.151 usecs Average: 2.628 usecs Max: 180.113 usecs Average: 2.559 usecs Max: 178.105 usecs
# Run 5 with 3.0 + patch
Wakeup Latency Average: 0.730 usecs Max: 8.037 usecs Average: 0.721 usecs Max: 16.613 usecs Average: 0.718 usecs Max: 16.613 usecs Average: 0.693 usecs Max: 58.095 usecs Average: 0.703 usecs Max: 11.078 usecs
So you can see that the patch does decrease both the Average and the max wakeup latency.
#include <sys/time.h> #include <stdio.h> #include <unistd.h> #include <sys/syscall.h> #include <time.h> #include <sys/sysinfo.h> #include <stdint.h> #include <sys/timerfd.h>
#define WORKLOAD_HIGH 100000 #define WORKLOAD_LOW 100
void worker() { int timerfd, ret; struct itimerspec new_value, old_value;
timerfd = timerfd_create(CLOCK_MONOTONIC, 0); if (timerfd == -1) { perror("timerfd_create"); return; }
new_value.it_value.tv_sec = 0; new_value.it_value.tv_nsec = 250000; new_value.it_interval.tv_sec = 0; new_value.it_interval.tv_nsec = 250000;
ret = timerfd_settime(timerfd, 0, &new_value, &old_value); if (ret == -1) { perror("timerfd_settime"); return; }
while (1) { int i, j, loops, event_count; uint64_t buf; for (i = 0; i < 10; ++i) { read(timerfd, &buf, sizeof(buf));
if (i == 0) loops = WORKLOAD_HIGH; else loops = WORKLOAD_LOW; for (j = 0; j < loops; ++j) /* burn cpu */; } } }
int main () { int i, nprocs; pid_t pid;
nprocs = get_nprocs(); for (i = 0; i < 2 * nprocs - 1; ++i) { pid = fork(); if (pid == 0) worker(); else if (pid == -1) perror("fork"); }
worker(); }
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