From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56831) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dBpru-0001NU-HA for qemu-devel@nongnu.org; Fri, 19 May 2017 17:55:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dBprp-00022L-Qr for qemu-devel@nongnu.org; Fri, 19 May 2017 17:55:30 -0400 Received: from [62.254.189.133] (port=54277 helo=centos.localdomain) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dBprp-0001qw-5U for qemu-devel@nongnu.org; Fri, 19 May 2017 17:55:25 -0400 From: Felipe Franciosi Date: Fri, 19 May 2017 22:29:50 +0100 Message-Id: <1495229390-18909-1-git-send-email-felipe@nutanix.com> Subject: [Qemu-devel] [PATCH] cpus: reset throttle_thread_scheduled after sleep List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , "Jason J. Herne" , Malcolm Crossley Cc: "qemu-devel@nongnu.org" , Felipe Franciosi Currently, the throttle_thread_scheduled flag is reset back to 0 before sleeping (as part of the throttling logic). Given that throttle_timer (well, any timer) may tick with a slight delay, it so happens that under heavy throttling (ie. close or on CPU_THROTTLE_PCT_MAX) the tick may schedule a further cpu_throttle_thread() work item after the flag reset, but before the previous sleep completed. This results on the vCPU thread sleeping continuously for potentially several seconds in a row. The chances of that happening can be drastically minimised by resetting the flag after the sleep. Signed-off-by: Felipe Franciosi Signed-off-by: Malcolm Crossley --- cpus.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/cpus.c b/cpus.c index 516e5cb..f42eebd 100644 --- a/cpus.c +++ b/cpus.c @@ -677,9 +677,9 @@ static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque) sleeptime_ns = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS); qemu_mutex_unlock_iothread(); - atomic_set(&cpu->throttle_thread_scheduled, 0); g_usleep(sleeptime_ns / 1000); /* Convert ns to us for usleep call */ qemu_mutex_lock_iothread(); + atomic_set(&cpu->throttle_thread_scheduled, 0); } static void cpu_throttle_timer_tick(void *opaque) -- 1.9.5