From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Chen, Kenneth W" Date: Mon, 13 Feb 2006 22:49:57 +0000 Subject: RE: PMU and timer interrupts Message-Id: <200602132249.k1DMnvg15069@unix-os.sc.intel.com> List-Id: References: <20060209171648.GA26865@frankl.hpl.hp.com> In-Reply-To: <20060209171648.GA26865@frankl.hpl.hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org Chen, Kenneth W wrote on Monday, February 13, 2006 12:32 PM > Stephane Eranian wrote on Monday, February 13, 2006 12:13 PM > > Jes seems to believe than this is more historical than anything for qla2xxx. > > Now what about the timer interrupt, why does it really need SA_INTERRUPT especially > > given that it is so high priority and with the TPR mechanism. IT seems to be > > a protection against MCA, IPI, IPI_RESCHEDULE based on the current layout. > > scheduler_tick function expects irq off because it calls load_balance and > will muck around with runqueue list. Won't that race with resched IPI if > irq is not masked? NO! Ken needs more coffee Monday morning .... I forgot that we don't check TIF_ flag when we are still on kernel stack. So resched IPI should be safe w.r.t timer interrupt because schedule is called after timer_interrupt finishes. - Ken