From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lu Baolu Subject: Re: [PATCHv4 2/2] iommu/vt-d: Limit number of faults to clear in irq handler Date: Thu, 3 May 2018 07:49:24 +0800 Message-ID: <5AEA4E84.6050609@linux.intel.com> References: <20180331003312.6390-1-dima@arista.com> <20180331003312.6390-2-dima@arista.com> <5AE95BFF.5040306@linux.intel.com> <1525264687.14025.20.camel@arista.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1525264687.14025.20.camel-nzgTgzXrdUbQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Dmitry Safonov , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org, "Raj, Ashok" Cc: David Woodhouse , 0x7f454c46-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Ingo Molnar , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: iommu@lists.linux-foundation.org Hi, On 05/02/2018 08:38 PM, Dmitry Safonov wrote: > Hi Lu, > > On Wed, 2018-05-02 at 14:34 +0800, Lu Baolu wrote: >> Hi, >> >> On 03/31/2018 08:33 AM, Dmitry Safonov wrote: >>> Theoretically, on some machines faults might be generated faster >>> than >>> they're cleared by CPU. >> Is this a real case? > No. 1/2 is a real case and this one was discussed on v3: > lkml.kernel.org/r/<20180215191729.15777-1-dima-nzgTgzXrdUbQT0dZR+AlfA@public.gmane.org> > > It's not possible on my hw as far as I tried, but the discussion result > was to fix this theoretical issue too. If faults are generated faster than CPU can clear them, the PCIe device should be in a very very bad state. How about disabling the PCIe device and ask the administrator to replace it? Anyway, I don't think that's goal of this patch series. :-) > >>> Let's limit the cleaning-loop by number of hw >>> fault registers. >> Will this cause the fault recording registers full of faults, hence >> new faults will be dropped without logging? > If faults come faster then they're being cleared - some of them will be > dropped without logging. Not sure if it's worth to report all faults in > such theoretical(!) situation. > If amount of reported faults for such situation is not enough and it's > worth to keep all the faults, then probably we should introduce a > workqueue here (which I did in v1, but it was rejected by the reason > that it will introduce some latency in fault reporting). > >> And even worse, new faults will not generate interrupts? > They will, we clear page fault overflow outside of the loop, so any new > fault will raise interrupt, iiuc. > I am afraid that they might not generate interrupts any more. Say, the fault registers are full of events that are not cleared, then a new fault comes. There is no room for this event and hence the hardware might drop it silently. Best regards, Lu Baolu