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SubjectRe: [PATCH] iommu: Lower severity of add/remove device messages
On 2020-03-27 1:02 pm, Ezequiel Garcia wrote:
> Hello Joerg,
> Thanks for reviewing.
> I understand this change bears some controversy
> for IOMMU, as developers are probably used to see these
> messages.
> On Fri, 2020-03-27 at 10:50 +0100, Joerg Roedel wrote:
>> On Mon, Mar 23, 2020 at 06:49:56PM -0300, Ezequiel Garcia wrote:
>>> These user messages are not really informational,
>>> but mostly of debug nature. Lower their severity.
>> Like most other messages in the kernel log, that is not a reason to
>> lower the severity.
>> These messages are the first thing to look at when
>> looking into IOMMU related issues.
> Sure, but the messages are still here, you can
> always enable them when you are looking at IOMMU issues :-)

That still begs the question of who "you" is and how they know they're
debugging an IOMMU issue in the first place. When all the developer has
to go on is a third-hand bugzilla attachment from a distro user's vague
report of graphics corruption/poor I/O performance/boot
failure/whatever, being able to tell straight away from a standard dmesg
dump whether an IOMMU is even in the picture or not saves a lot of
protracted back-and-forth for everyone involved.
> The idea is to reduce the amount of verbosity in the kernel.

Under what justification? Users with slow consoles or who just want a
quiet boot are already free to turn down the loglevel; a handful of
messages at boot-time and device hotplug seem hardly at risk of drowning
out all the systemd audit spam anyway. Note that the IOMMU subsystem is
by nature a little atypical as a lot of what it does is only visible as
secondary effects on other drivers and subsystems, without their
explicit involvement or knowledge. In that respect, hiding its activity
can arguably lead to more non-obvious situations than many other subsystems.

> If all subsystems would print messages that are useful
> when looking at issues, things would be quite nasty verbose.

From a personal standpoint, can we at least eradicate all the "Hi! I'm
a driver/subsystem you don't even have the hardware for!" messages
first, then maybe come back and reconsider the ones that convey actual
information later?


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