From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50756) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1csOzT-0006fr-3P for qemu-devel@nongnu.org; Mon, 27 Mar 2017 03:23:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1csOzS-00036W-5f for qemu-devel@nongnu.org; Mon, 27 Mar 2017 03:22:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59886) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1csOzR-00036D-Vd for qemu-devel@nongnu.org; Mon, 27 Mar 2017 03:22:58 -0400 From: Peter Xu Date: Mon, 27 Mar 2017 15:21:28 +0800 Message-Id: <1490599288-11751-6-git-send-email-peterx@redhat.com> In-Reply-To: <1490599288-11751-1-git-send-email-peterx@redhat.com> References: <1490599288-11751-1-git-send-email-peterx@redhat.com> Subject: [Qemu-devel] [PATCH 5/5] cpu: throttle: fix throttle time slice List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Juan Quintela , "\\ Dr . David Alan Gilbert \\ " , peterx@redhat.com, Paolo Bonzini , Richard Henderson , "Jason J . Herne" IIUC the throttle idea is that: we split a CPU_THROTTLE_TIMESLICE_NS time slice into two parts - one for vcpu, one for throttle thread (which will suspend the thread by a sleep). However current algorithm on calculating the working piece and sleeping piece is strange. Assume a 99% throttle, what we want is to merely stop vcpu from running, but the old logic will just first let the vcpu run for a very long time (which is "CPU_THROTTLE_TIMESLICE_NS / (1-pct)" = 1 second) before doing anything else. Fixing it up to the simplest but imho accurate logic. CC: Paolo Bonzini CC: Richard Henderson CC: Jason J. Herne Signed-off-by: Peter Xu --- cpus.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/cpus.c b/cpus.c index 167d961..7976ce4 100644 --- a/cpus.c +++ b/cpus.c @@ -633,7 +633,6 @@ static const VMStateDescription vmstate_timers = { static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque) { double pct; - double throttle_ratio; long sleeptime_ns; if (!cpu_throttle_get_percentage()) { @@ -641,8 +640,7 @@ static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque) } pct = (double)cpu_throttle_get_percentage()/100; - throttle_ratio = pct / (1 - pct); - sleeptime_ns = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS); + sleeptime_ns = (long)((1 - pct) * CPU_THROTTLE_TIMESLICE_NS); qemu_mutex_unlock_iothread(); atomic_set(&cpu->throttle_thread_scheduled, 0); @@ -668,7 +666,7 @@ static void cpu_throttle_timer_tick(void *opaque) pct = (double)cpu_throttle_get_percentage()/100; timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) + - CPU_THROTTLE_TIMESLICE_NS / (1-pct)); + CPU_THROTTLE_TIMESLICE_NS * pct); } void cpu_throttle_set(int new_throttle_pct) -- 2.7.4