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Re: [Xen-devel] [PATCH v3 14/14] AMD/IOMMU: process softirqs while dumping IRTs


  • To: Jan Beulich <JBeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 19 Jul 2019 18:55:50 +0100
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  • Cc: Brian Woods <brian.woods@xxxxxxx>, Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
  • Delivery-date: Fri, 19 Jul 2019 17:56:01 +0000
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On 16/07/2019 17:41, Jan Beulich wrote:
> When there are sufficiently many devices listed in the ACPI tables (no
> matter if they actually exist), output may take way longer than the
> watchdog would like.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v3: New.
> ---
> TBD: Seeing the volume of output I wonder whether we should further
>       suppress logging headers of devices which have no active entry
>       (i.e. emit the header only upon finding the first IRTE worth
>       logging). And while minor for the total volume of output I'm
>       also unconvinced logging both a "per device" header line and a
>       "shared" one makes sense, when only one of the two can actually
>       be followed by actual contents.

I don't have a system I can access at the moment, so can't judge how bad
it is right now.  However, I would advocate the removal of irrelevant
information.

Either way, this is debugging so Acked-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>

As an observation, I wonder whether continually sprinkling
process_pending_softirqs() is the best thing to do for keyhandlers. 
We've got a number of other which incur the wrath of the watchdog (grant
table in particular), which in practice means they are typically broken
when they are actually used for debugging production.

As these are for debugging only, might it be a better idea to stop the
watchdog while keyhandlers are running?  The only useful thing we
actually manage here is to stop the watchdog killing us.

~Andrew

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