On Fri, 2012-10-12 at 22:52 +0200, Thomas Gleixner wrote: > On Fri, 12 Oct 2012, Liu, Chuansheng wrote: > > > -----Original Message----- > > > From: anish kumar [mailto:anish198519851...@gmail.com] > > > Sent: Friday, October 12, 2012 11:25 PM > > > To: Liu, Chuansheng > > > Cc: Thomas Gleixner; linux-kernel@vger.kernel.org > > > Subject: RE: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support with > > > irq > > > thread > > > > > > On Fri, 2012-10-12 at 14:57 +0000, Liu, Chuansheng wrote: > > > > > On SMP an interrupt which is raised after the ack() again before the > > > > > handler finishes, can invoke another delivery on a different CPU, > > > > > which then sees the IRQ_INPROGESS flag, masks it and flags it > > > > > PENDING. When the primary handler on the first CPU returns, it sees > > > > > the PENDING flag, unmasks and invokes the handler another time. > > > > In this case, when IRQ_INPROGRESS flag is set, on another CPU, it will > > > > mask and ack it, if before the primary handler on the first CPU returns, > > > > the edge interrupt is raised again, it will be lost, right? > > > Why will the interrupt be raised again?Is not it masked?I read tglx > > I means because it is masked, if at this time device issues edge irq, > > It will not be delivered and lost. > > No, it is NOT lost. The irq is marked PENDING already, so we invoke It is fairly easy for an edge triggered interrupt to be missed - for example if interrupts have to be masked for a period - and unless there is some type of hardware latch that records the event it is impossible to recover. tglx, explanation will only work if we have a hardware latch which when unmasked sends all those edge interrupts again (which had come when it was masked while the CPU was handling the same interrupts).
PS:http://kernel.org/doc/htmldocs/genericirq.html > the handler again and handle it. And before we invoke the handler > another time we unmask it. > > It does not matter at all whether the interrupt has been sent five > times while it was masked. What matters is that we recorded the first > one and set the PENDING flag. That way we invoke the interrupt handler > again and keep stuff rolling. > > Thanks, > > tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/