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linux: make timerfd_settime(2) set expirations count to zero

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On Linux, read(2) from a timerfd file descriptor returns an unsigned
8-byte integer (uint64_t) containing the number of expirations
that have occurred, if the timer has already expired one or more
times since its settings were last modified using timerfd_settime(),
or since the last successful read(2).  That's to say, once we do
a read or call timerfd_settime(), timer fd's expiration count should
be zero.  Some Linux applications create timerfd and add it to epoll
with LT mode, when event comes, they do timerfd_settime instead
of read to stop event source from trigger.  On FreeBSD,
timerfd_settime(2) didn't set the count to zero, which caused high
CPU utilization.

Submitted by:	ankohuu_outlook.com (Shunchao Hu)
Differential Revision: https://reviews.freebsd.org/D28231
This commit is contained in:
shu 2021-02-03 16:51:45 +00:00 committed by Edward Tomasz Napierala
parent 43e083be81
commit ae71b794cb
1 changed files with 1 additions and 0 deletions
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1
sys/compat/linux/linux_event.c
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@ -981,6 +981,7 @@ linux_timerfd_settime(struct thread *td, struct linux_timerfd_settime_args *args
linux_timerfd_curval(tfd, &ots);
tfd->tfd_time = nts;
tfd->tfd_count = 0;
if (timespecisset(&nts.it_value)) {
linux_timerfd_clocktime(tfd, &cts);
ts = nts.it_value;