From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: [RFC][PATCH] Register Linux dyntick timer as per-thread signal Date: Thu, 16 Jun 2011 11:31:42 +0200 Message-ID: <4DF9CD7E.5020509@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: kvm , Paolo Bonzini , Ingo Molnar , Sasha Levin To: qemu-devel , Anthony Liguori Return-path: Received: from david.siemens.de ([192.35.17.14]:18823 "EHLO david.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754250Ab1FPJb7 (ORCPT ); Thu, 16 Jun 2011 05:31:59 -0400 Sender: kvm-owner@vger.kernel.org List-ID: 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 using this pattern so far. But Linux provides a (non-portable) way to restrict the signal to a single thread: 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. Signed-off-by: Jan Kiszka --- compatfd.c | 11 +++++++++++ compatfd.h | 1 + qemu-timer.c | 12 +++++++++++- 3 files changed, 23 insertions(+), 1 deletions(-) diff --git a/compatfd.c b/compatfd.c index 41586ce..31654c6 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 fc37915..6b04877 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 72066c7..09e6f17 100644 --- a/qemu-timer.c +++ b/qemu-timer.c @@ -803,6 +803,8 @@ 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; @@ -821,8 +823,16 @@ 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; ev.sigev_signo = SIGALRM; +#ifdef SIGEV_THREAD_ID + if (qemu_signalfd_available()) { + ev.sigev_notify = SIGEV_THREAD_ID; + ev._sigev_un._tid = qemu_get_thread_id(); + } else +#endif /* SIGEV_THREAD_ID */ + { + ev.sigev_notify = SIGEV_SIGNAL; + } if (timer_create(CLOCK_REALTIME, &ev, &host_timer)) { perror("timer_create"); -- 1.7.1