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trivial: doc: hpfall: reduce risk that hpfall can do harm

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Improve the example code to be at least useable, as in not causing
harm (as shown below). Code can still be improved further, but this
adds some basic safeguards.

1. hpfall *MUST* mlockall(MCL_CURRENT|MCL_FUTURE); itself!
Since the Program sits and waits most of the time it becomes very likely
swapped out. If it gets woken up when the laptop drops from the table
while it is swapped out it actually triggers harddrive activity!

2. Daemonize hpfall using 'daemon(0,0)' (quick and dirty).

3. Give hpfall realtime priority.
Should give a chance that it has less latency when woken up.

Signed-off-by: Christian Thaeter <ct@pipapo.org>
Signed-off-by: Frans Pop <elendil@planet.nl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Christian Thaeter 2009-07-25 20:55:15 +02:00 committed by Jiri Kosina
parent 8103b5cc62
commit 2bace8b951
1 changed files with 8 additions and 0 deletions
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8
Documentation/hwmon/hpfall.c
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@ -16,6 +16,8 @@
#include <stdint.h>
#include <errno.h>
#include <signal.h>
#include <sys/mman.h>
#include <sched.h>
void write_int(char *path, int i)
{
@ -62,6 +64,7 @@ void ignore_me(void)
int main(int argc, char *argv[])
{
int fd, ret;
struct sched_param param;
fd = open("/dev/freefall", O_RDONLY);
if (fd < 0) {
@ -69,6 +72,11 @@ int main(int argc, char *argv[])
return EXIT_FAILURE;
}
daemon(0, 0);
param.sched_priority = sched_get_priority_max(SCHED_FIFO);
sched_setscheduler(0, SCHED_FIFO, &param);
mlockall(MCL_CURRENT|MCL_FUTURE);
signal(SIGALRM, ignore_me);
for (;;) {