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From: Lu Baolu <>
To: Dmitry Safonov <>,,, "Raj,
	Ashok" <>
	Alex Williamson <>,
	David Woodhouse <>,
	Ingo Molnar <>,
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	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>


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:
> 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

  reply	other threads:[~2018-05-02 23:49 UTC|newest]

Thread overview: 15+ 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 ` [PATCHv4 2/2] iommu/vt-d: Limit number of faults to clear in irq handler Dmitry Safonov
2018-05-02  6:34   ` Lu Baolu
2018-05-02 12:38     ` Dmitry Safonov
2018-05-02 23:49       ` Lu Baolu [this message]
2018-05-03  0:52         ` Dmitry Safonov
2018-05-03  1:32           ` Lu Baolu
2018-05-03  1:59             ` Dmitry Safonov
2018-05-03  2:16               ` Lu Baolu
2018-05-03  2:32                 ` Lu Baolu
2018-05-03  2:34                 ` Dmitry Safonov
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
2018-05-03 12:40   ` Joerg Roedel
2018-05-03 16:12     ` Dmitry Safonov

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