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xstat: prevent CPU loop when -period 0

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Historically xstat_cm_test and xstat_fs_test have supported option
'-period <mm>' to specify continuous operaiton for a length of time.  If
'-period 0' was specified, both programs exited immediately.

Beginning with commits 2c1a7e4733 'xstat:
add xstat_*_Wait functions' and 6b67cac432
'convert xstat and friends to pthreads', xstat_cm_test and xstat_fs_test
now support -period 0 to run "forever".  This support is implemented in
xstat_cm_Wait and xstat_fs_Wait, respectively.  Although the "wait
forever" logic was added to allow consolidation of similar code in
afsmonitor, it also changed how xstat_cm_test and xstat_fs_test behave
for '-period 0'.

Unfortunately, there is a bug in this support, at least when running on
pthreads.  After the initial 24 minute timer expires, the while (1) will
repeatedly run select with a timeout that is now 0.  This causes the
while loop to consume 100% of the CPU on which this thread is
dispatched.

Instead, modify the wait-forever logic to specify NULL for the select()
timeout value.  Also update the man page to document that '-period 0'
means forever.

Change-Id: I25d0d5be0eedb8bf3de495785b9b03a3e3d45221
Reviewed-on: https://gerrit.openafs.org/14366
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
This commit is contained in:
Mark Vitale 2020-09-18 12:46:57 -04:00 committed by Benjamin Kaduk
parent 74f46e0912
commit 4e85324729
3 changed files with 4 additions and 7 deletions
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3
doc/man-pages/pod1/xstat_fs_test.pod
View File

@ -94,7 +94,8 @@ Cache Manager. The default is 30 seconds.
=item B<-period> <I<data collection time>>
Sets the number of minutes the program runs; at the end of this period of
time, the program exits. The default is 10 minutes.
time, the program exits. The default is 10 minutes. Period 0 means run
forever.
=item B<-debug>

4
src/xstat/xstat_cm.c
View File

@ -662,8 +662,6 @@ xstat_cm_Wait(int sleep_secs)
}
} else if (sleep_secs == 0) {
/* Sleep forever. */
tv.tv_sec = 24 * 60;
tv.tv_usec = 0;
if (xstat_cm_debug)
fprintf(stderr, "[%s] going to sleep ...\n", rn);
while (1) {
@ -671,7 +669,7 @@ xstat_cm_Wait(int sleep_secs)
0, /*Descriptors ready for reading */
0, /*Descriptors ready for writing */
0, /*Descriptors with exceptional conditions */
&tv); /*Timeout structure */
NULL); /* NULL timeout means "forever" */
if (code < 0) {
fprintf(stderr, "[%s] select() error %d\n", rn, errno);
break;

4
src/xstat/xstat_fs.c
View File

@ -856,8 +856,6 @@ xstat_fs_Wait(int sleep_secs)
}
} else if (sleep_secs == 0) {
/* Sleep forever. */
tv.tv_sec = 24 * 60;
tv.tv_usec = 0;
if (xstat_fs_debug)
fprintf(stderr, "[ %s ] going to sleep ...\n", rn);
while (1) {
@ -865,7 +863,7 @@ xstat_fs_Wait(int sleep_secs)
0, /*Descriptors ready for reading */
0, /*Descriptors ready for writing */
0, /*Descriptors with exceptional conditions */
&tv); /*Timeout structure */
NULL); /* NULL timeout means "forever" */
if (code < 0) {
fprintf(stderr, "[%s] select() error %d\n", rn, errno);
break;