On Thursday 18 of October 2012 17:12:20 Youquan Song wrote:
>
> V2: Add menu timer status enums depends on Rafael suggestion.
>
> The prediction for future is difficult and when the cpuidle governor prediction
> fails and govenor possibly choose the shallower C-state than it should. How to
> quickly notice and find the failure becomes important for power saving.
>
> cpuidle menu governor has a method to predict the repeat pattern if there are 8
> C-states residency which are continuous and the same or very close, so it will
> predict the next C-states residency will keep same residency time.
>
> This patchset adds a timer when menu governor choose a non-deepest C-state in
> order to wake up quickly from shallow C-state to avoid staying too long at
> shallow C-state for prediction failure. The timer is set to a time out value
> that is greater than predicted time and if the timer with the value is triggered
> , we can confidently conclude prediction is failure. When prediction
> succeeds, CPU is waken up from C-states in predicted time and the timer is not
> triggered and will be cancelled right after CPU waken up. When prediction fails,
> the timer is triggered to wake up CPU from shallow C-states, so menu governor
> will quickly notice that prediction fails and then re-evaluates deeper C-states
> possibility. This patchset can improves cpuidle prediction process for both
> repeat mode and general mode.
>
> The patchset integrates one patch from Rik van Riel <riel@xxxxxxxxxx>, which try
> to find a typical interval along with cut the upside outliers depends on
> historical sleep intervals. The patch tends to choose a shallow C-state to
> achieve better performance and ehancement of prediction failure will advise it
> if the deepest C-state should be chosen.
>
> Testing result:
>
> The whole patchset achieve good result after bunch of testing/tuning.
> Testing on two sockets Sandybridge server, SPECPower2008 get 2%~5% increase
> ssj_ops/watt; Running benchmark in phoronix-test-suite: compress-7zip,
> build-linux-kernel, apache, fio etc, it also proves to increase the
> performance/power; What's more, it not only boosts the performance but also
> saves power.
>
> There are also 2 cases will clear show this patchset benefit.
>
> One case is turbostat utility (tools/power/x86/turbostat) at kernel 3.3 or early
> . turbostat utility will read 10 registers one by one at Sandybridge, so it will
> generate 10 IPIs to wake up idle CPUs. So cpuidle menu governor will predict it
> is repeat mode and there is another IPI wake up idle CPU soon, so it keeps idle
> CPU stay at C1 state even though CPU is totally idle. However, in the turbostat
> , following 10 registers reading is sleep 5 seconds by default, so the idle CPU
> will keep at C1 for a long time though it is idle until break event occurs.
> In a idle Sandybridge system, run "./turbostat -v", we will notice that deep
> C-state dangles between "70% ~ 99%". After patched the kernel, we will notice
> deep C-state stays at >99.98%.
>
> Below is another case which will clearly show the patch much benefit:
>
> #include <stdlib.h>
> #include <stdio.h>
> #include <unistd.h>
> #include <signal.h>
> #include <sys/time.h>
> #include <time.h>
> #include <pthread.h>
>
> volatile int * shutdown;
> volatile long * count;
> int delay = 20;
> int loop = 8;
>
> void usage(void)
> {
> fprintf(stderr,
> "Usage: idle_predict [options]\n"
> " --help -h Print this help\n"
> " --thread -n Thread number\n"
> " --loop -l Loop times in shallow Cstate\n"
> " --delay -t Sleep time (uS)in shallow Cstate\n");
> }
>
> void *simple_loop() {
> int idle_num = 1;
> while (!(*shutdown)) {
> *count = *count + 1;
>
> if (idle_num % loop)
> usleep(delay);
> else {
> /* sleep 1 second */
> usleep(1000000);
> idle_num = 0;
> }
> idle_num++;
> }
>
> }
>
> static void sighand(int sig)
> {
> *shutdown = 1;
> }
>
> int main(int argc, char *argv[])
> {
> sigset_t sigset;
> int signum = SIGALRM;
> int i, c, er = 0, thread_num = 8;
> pthread_t pt[1024];
>
> static char optstr[] = "n:l:t:h:";
>
> while ((c = getopt(argc, argv, optstr)) != EOF)
> switch (c) {
> case 'n':
> thread_num = atoi(optarg);
> break;
> case 'l':
> loop = atoi(optarg);
> break;
> case 't':
> delay = atoi(optarg);
> break;
> case 'h':
> default:
> usage();
> exit(1);
> }
>
> printf("thread=%d,loop=%d,delay=%d\n",thread_num,loop,delay);
> count = malloc(sizeof(long));
> shutdown = malloc(sizeof(int));
> *count = 0;
> *shutdown = 0;
>
> sigemptyset(&sigset);
> sigaddset(&sigset, signum);
> sigprocmask (SIG_BLOCK, &sigset, NULL);
> signal(SIGINT, sighand);
> signal(SIGTERM, sighand);
>
> for(i = 0; i < thread_num ; i++)
> pthread_create(&pt[i], NULL, simple_loop, NULL);
>
> for (i = 0; i < thread_num; i++)
> pthread_join(pt[i], NULL);
>
> exit(0);
> }
>
> Get powertop v2 from git://github.com/fenrus75/powertop, build powertop.
> After build the above test application, then run it.
> Test plaform can be Intel Sandybridge or other recent platforms.
> #./idle_predict -l 10 &
> #./powertop
>
> We will find that deep C-state will dangle between 40%~100% and much time spent
> on C1 state. It is because menu governor wrongly predict that repeat mode
> is kept, so it will choose the C1 shallow C-state even though it has chance to
> sleep 1 second in deep C-state.
>
> While after patched the kernel, we find that deep C-state will keep >99.6%.
>
> Thanks for help from Arjan, Len Brown and Rik!
All patches applied to linux-pm.git/linux-next as v3.8 material.
Thanks,
Rafael
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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