From: Dmitry Safonov <dima@arista.com> To: Lu Baolu <baolu.lu@linux.intel.com>, linux-kernel@vger.kernel.org, joro@8bytes.org, "Raj, Ashok" <ashok.raj@intel.com> Cc: 0x7f454c46@gmail.com, Alex Williamson <alex.williamson@redhat.com>, David Woodhouse <dwmw2@infradead.org>, Ingo Molnar <mingo@kernel.org>, iommu@lists.linux-foundation.org Subject: Re: [PATCHv4 2/2] iommu/vt-d: Limit number of faults to clear in irq handler Date: Wed, 02 May 2018 13:38:07 +0100 [thread overview] Message-ID: <1525264687.14025.20.camel@arista.com> (raw) In-Reply-To: <5AE95BFF.5040306@linux.intel.com> 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@arista.com> It's not possible on my hw as far as I tried, but the discussion result was to fix this theoretical issue too. > > > 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. -- Thanks, Dmitry
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From: Dmitry Safonov via iommu <iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org> To: Lu Baolu <baolu.lu-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org, "Raj, Ashok" <ashok.raj-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> Cc: David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, 0x7f454c46-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Subject: Re: [PATCHv4 2/2] iommu/vt-d: Limit number of faults to clear in irq handler Date: Wed, 02 May 2018 13:38:07 +0100 [thread overview] Message-ID: <1525264687.14025.20.camel@arista.com> (raw) In-Reply-To: <5AE95BFF.5040306-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> 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. > > > 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. -- Thanks, Dmitry
next prev parent reply other threads:[~2018-05-02 12:38 UTC|newest] Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-03-31 0:33 [PATCHv4 1/2] iommu/vt-d: Ratelimit each dmar fault printing Dmitry Safonov 2018-03-31 0:33 ` Dmitry Safonov via iommu 2018-03-31 0:33 ` [PATCHv4 2/2] iommu/vt-d: Limit number of faults to clear in irq handler Dmitry Safonov 2018-03-31 0:33 ` Dmitry Safonov via iommu 2018-05-02 6:34 ` Lu Baolu 2018-05-02 6:34 ` Lu Baolu 2018-05-02 12:38 ` Dmitry Safonov [this message] 2018-05-02 12:38 ` Dmitry Safonov via iommu 2018-05-02 23:49 ` Lu Baolu 2018-05-02 23:49 ` Lu Baolu 2018-05-03 0:52 ` Dmitry Safonov 2018-05-03 0:52 ` Dmitry Safonov via iommu 2018-05-03 1:32 ` Lu Baolu 2018-05-03 1:32 ` Lu Baolu 2018-05-03 1:59 ` Dmitry Safonov 2018-05-03 1:59 ` Dmitry Safonov via iommu 2018-05-03 2:16 ` Lu Baolu 2018-05-03 2:16 ` Lu Baolu 2018-05-03 2:32 ` Lu Baolu 2018-05-03 2:32 ` Lu Baolu 2018-05-03 2:34 ` Dmitry Safonov 2018-05-03 2:34 ` Dmitry Safonov via iommu 2018-05-03 2:44 ` Lu Baolu 2018-05-03 2:44 ` Lu Baolu 2018-05-02 2:22 ` [PATCHv4 1/2] iommu/vt-d: Ratelimit each dmar fault printing Dmitry Safonov 2018-05-02 2:22 ` Dmitry Safonov via iommu 2018-05-03 12:40 ` Joerg Roedel 2018-05-03 16:12 ` Dmitry Safonov 2018-05-03 16:12 ` Dmitry Safonov via iommu
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