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Register Linux dyntick timer as per-thread signal

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Derived from kvm-tool patch
http://thread.gmane.org/gmane.comp.emulators.kvm.devel/74309

Ingo Molnar pointed out that sending the timer signal to the whole
process, just blocking it everywhere, is suboptimal with an increasing
number of threads. QEMU is also using this pattern so far.

Linux provides a (non-portable) way to restrict the signal to a single
thread: We can use SIGEV_THREAD_ID unless we are forced to emulate
signalfd via an additional thread. That case could theoretically be
optimized as well, but it doesn't look worth bothering.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Jan Kiszka 2011-06-17 11:25:49 +02:00 committed by Anthony Liguori
parent 17604dac28
commit d25f89c9e9
3 changed files with 20 additions and 0 deletions
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11
compatfd.c
View File

@ -115,3 +115,14 @@ int qemu_signalfd(const sigset_t *mask)
return qemu_signalfd_compat(mask);
}
bool qemu_signalfd_available(void)
{
#ifdef CONFIG_SIGNALFD
errno = 0;
syscall(SYS_signalfd, -1, NULL, _NSIG / 8);
return errno != ENOSYS;
#else
return false;
#endif
}

1
compatfd.h
View File

@ -39,5 +39,6 @@ struct qemu_signalfd_siginfo {
};
int qemu_signalfd(const sigset_t *mask);
bool qemu_signalfd_available(void);
#endif

8
qemu-timer.c
View File

@ -831,6 +831,8 @@ static int64_t qemu_next_alarm_deadline(void)
#if defined(__linux__)
#include "compatfd.h"
static int dynticks_start_timer(struct qemu_alarm_timer *t)
{
struct sigevent ev;
@ -850,6 +852,12 @@ static int dynticks_start_timer(struct qemu_alarm_timer *t)
memset(&ev, 0, sizeof(ev));
ev.sigev_value.sival_int = 0;
ev.sigev_notify = SIGEV_SIGNAL;
#ifdef SIGEV_THREAD_ID
if (qemu_signalfd_available()) {
ev.sigev_notify = SIGEV_THREAD_ID;
ev._sigev_un._tid = qemu_get_thread_id();
}
#endif /* SIGEV_THREAD_ID */
ev.sigev_signo = SIGALRM;
if (timer_create(CLOCK_REALTIME, &ev, &host_timer)) {