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authorJan Kiszka <jan.kiszka@siemens.com>2011-06-17 11:25:49 +0200
committerAnthony Liguori <aliguori@us.ibm.com>2011-07-23 11:26:12 -0500
commitd25f89c9e91d6c46b85969922411a211a6347a7d (patch)
tree6ef37246ff23527e8bc62fcf4f271bded16619d3
parentmc146818rtc: Handle host clock resets (diff)
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Register Linux dyntick timer as per-thread signal
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>
-rw-r--r--compatfd.c11
-rw-r--r--compatfd.h1
-rw-r--r--qemu-timer.c8
3 files changed, 20 insertions, 0 deletions
diff --git a/compatfd.c b/compatfd.c
index 41586ceae..31654c62a 100644
--- a/compatfd.c
+++ b/compatfd.c
@@ -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
+}
diff --git a/compatfd.h b/compatfd.h
index fc3791520..6b04877b9 100644
--- a/compatfd.h
+++ b/compatfd.h
@@ -39,5 +39,6 @@ struct qemu_signalfd_siginfo {
};
int qemu_signalfd(const sigset_t *mask);
+bool qemu_signalfd_available(void);
#endif
diff --git a/qemu-timer.c b/qemu-timer.c
index f95374c7c..30e8f1272 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -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)) {