From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756104Ab0DFPb3 (ORCPT ); Tue, 6 Apr 2010 11:31:29 -0400 Received: from fg-out-1718.google.com ([72.14.220.154]:29576 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750976Ab0DFPbY (ORCPT ); Tue, 6 Apr 2010 11:31:24 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=R7mWb3L1WGbwSfj/j5Cdbm2v/KmuFzT9u+mZNllG6UvVNQRe7YCCRcduyLPh98zt1t S6das9S3GNYwlKsHfI36W8Xp/jOOCMXUDn2BveipZfRLgImTJFGNNyIF+JgGVHBt5i+/ KlBDiRQwPY1rsXGWJyNGwmVpx4GhA4/zd4F/I= Date: Tue, 6 Apr 2010 19:31:15 +0400 From: Cyrill Gorcunov To: Frederic Weisbecker Cc: Don Zickus , mingo@elte.hu, peterz@infradead.org, aris@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [watchdog] combine nmi_watchdog and softlockup Message-ID: <20100406153115.GB5744@lenovo> References: <20100323213338.GA29170@redhat.com> <20100406141321.GA8416@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100406141321.GA8416@nowhere> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 06, 2010 at 04:13:30PM +0200, Frederic Weisbecker wrote: [...] > > +static int watchdog_enable(int cpu) > > +{ > > + struct perf_event_attr *wd_attr; > > + struct perf_event *event = per_cpu(watchdog_ev, cpu); > > + struct task_struct *p = per_cpu(softlockup_watchdog, cpu); > > + > > + /* is it already setup and enabled? */ > > + if (event && event->state > PERF_EVENT_STATE_OFF) > > + goto out; > > + > > + /* it is setup but not enabled */ > > + if (event != NULL) > > + goto out_enable; > > + > > + /* Try to register using hardware perf events first */ > > + wd_attr = &wd_hw_attr; > > + wd_attr->sample_period = hw_nmi_get_sample_period(); > > + event = perf_event_create_kernel_counter(wd_attr, cpu, -1, watchdog_overflow_callback); > > + if (!IS_ERR(event)) { > > + printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.\n"); > > + goto out_save; > > + } > > + > > + /* hardware doesn't exist or not supported, fallback to software events */ > > + printk(KERN_INFO "NMI watchdog: hardware not available, trying software events\n"); > > + wd_attr = &wd_sw_attr; > > + wd_attr->sample_period = softlockup_thresh * NSEC_PER_SEC; > > + event = perf_event_create_kernel_counter(wd_attr, cpu, -1, watchdog_overflow_callback); > > I fear the cpu clock is not going to help you detecting any hard lockups. > If you're stuck in an interrupt or an irq disabled loop, your cpu clock is > not going to fire. > I guess it's not supposed to. For such cases only nmi irqs may help for which the perf events are there (/me need to check if we program apic timer for anything like that). But it should help for other deadlocks. Or I miss something? -- Cyrill