From patchwork Fri Jun 1 10:01:02 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Mackerras X-Patchwork-Id: 162303 X-Patchwork-Delegate: paulus@samba.org Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from ozlabs.org (localhost [IPv6:::1]) by ozlabs.org (Postfix) with ESMTP id B2F80B733B for ; Fri, 1 Jun 2012 20:21:25 +1000 (EST) Received: by ozlabs.org (Postfix) id AF739B700F; Fri, 1 Jun 2012 20:20:29 +1000 (EST) Delivered-To: linuxppc-dev@ozlabs.org Received: by ozlabs.org (Postfix, from userid 1003) id 9AA96B700B; Fri, 1 Jun 2012 20:20:29 +1000 (EST) Date: Fri, 1 Jun 2012 20:01:02 +1000 From: Paul Mackerras To: linuxppc-dev@ozlabs.org Subject: [PATCH] powerpc/time: Sanity check of decrementer expiration is necessary Message-ID: <20120601100102.GA11714@pale.ozlabs.ibm.com> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Cc: Anton Blanchard X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org This reverts 68568add2c ("powerpc/time: Remove unnecessary sanity check of decrementer expiration"). We do need to check whether we have reached the expiration time of the next event, because we sometimes get an early decrementer interrupt, most notably when we set the decrementer to 1 in arch_irq_work_raise(). The effect of not having the sanity check is that if timer_interrupt() gets called early, we leave the decrementer set to its maximum value, which means we then don't get any more decrementer interrupts for about 4 seconds (or longer, depending on timebase frequency). I saw these pauses as a consequence of getting a stray hypervisor decrementer interrupt left over from exiting a KVM guest. This isn't quite a straight revert because of changes to the surrounding code, but it restores the same algorithm as was previously used. Cc: stable@kernel.org Cc: Anton Blanchard Acked-by: Benjamin Herrenschmidt Signed-off-by: Paul Mackerras Acked-by: Anton Blanchard --- If there are no objections, I'll send this to Linus shortly. This regression is present in 3.3 and 3.4 as well as current upstream. arch/powerpc/kernel/time.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index 99a995c..be171ee 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -475,6 +475,7 @@ void timer_interrupt(struct pt_regs * regs) struct pt_regs *old_regs; u64 *next_tb = &__get_cpu_var(decrementers_next_tb); struct clock_event_device *evt = &__get_cpu_var(decrementers); + u64 now; /* Ensure a positive value is written to the decrementer, or else * some CPUs will continue to take decrementer exceptions. @@ -509,9 +510,16 @@ void timer_interrupt(struct pt_regs * regs) irq_work_run(); } - *next_tb = ~(u64)0; - if (evt->event_handler) - evt->event_handler(evt); + now = get_tb_or_rtc(); + if (now >= *next_tb) { + *next_tb = ~(u64)0; + if (evt->event_handler) + evt->event_handler(evt); + } else { + now = *next_tb - now; + if (now <= DECREMENTER_MAX) + set_dec((int)now); + } #ifdef CONFIG_PPC64 /* collect purr register values often, for accurate calculations */