From: Keir Fraser Date: Wed, 3 Sep 2008 10:02:57 +0000 (+0100) Subject: Fix for VCPU periodic timer. X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~14111^2~53 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=04250df04652b746cf77e87aa52e4048d06e4062;p=xen.git Fix for VCPU periodic timer. Idle vcpu periodic timer is useless. It increased the lapic timer interrupt number, which decreased the cpu idle residency. This patch disables idle vcpu periodic timer via keeping v->periodic_period = 0. The vcpu periodic timer may be expired 50us before expected time because there is a 50us TIMER_SLOP used for soft timer (xen/common/timer.c, timer_softirq_action()). This will cause vcpu_periodic_timer_work() be continuously called tens of times in a single call of timer_softirq_action() until (now > periodic_next_event). It brings unnecessary overhead. This patch adds a similar time slop in vcpu periodic timer to eliminate this overhead. Signed-off-by: Wei Gang --- diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c index 1dc24924e6..10d0cef7c6 100644 --- a/xen/arch/x86/domain.c +++ b/xen/arch/x86/domain.c @@ -302,7 +302,8 @@ int vcpu_initialise(struct vcpu *v) else { /* PV guests by default have a 100Hz ticker. */ - v->periodic_period = MILLISECS(10); + if ( !is_idle_domain(d) ) + v->periodic_period = MILLISECS(10); /* PV guests get an emulated PIT too for video BIOSes to use. */ if ( !is_idle_domain(d) && (v->vcpu_id == 0) ) diff --git a/xen/common/schedule.c b/xen/common/schedule.c index 2934d07029..7d32c99485 100644 --- a/xen/common/schedule.c +++ b/xen/common/schedule.c @@ -628,7 +628,9 @@ static void vcpu_periodic_timer_work(struct vcpu *v) return; periodic_next_event = v->periodic_last_event + v->periodic_period; - if ( now > periodic_next_event ) + + /* The timer subsystem may call us up to TIME_SLOP ahead of deadline. */ + if ( (now + TIME_SLOP) > periodic_next_event ) { send_timer_event(v); v->periodic_last_event = now;