[PATCH] iommu: Lower severity of add/remove device messages

[PATCH] iommu: Lower severity of add/remove device messages

[Ezequiel Garcia]

These user messages are not really informational,
but mostly of debug nature. Lower their severity.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
---
 drivers/iommu/iommu.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 3e3528436e0b..1ebd17033714 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -758,7 +758,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
 
 	trace_add_device_to_group(group->id, dev);
 
-	dev_info(dev, "Adding to iommu group %d\n", group->id);
+	dev_dbg(dev, "Adding to iommu group %d\n", group->id);
 
 	return 0;
 
@@ -792,7 +792,7 @@ void iommu_group_remove_device(struct device *dev)
 	struct iommu_group *group = dev->iommu_group;
 	struct group_device *tmp_device, *device = NULL;
 
-	dev_info(dev, "Removing from iommu group %d\n", group->id);
+	dev_dbg(dev, "Removing from iommu group %d\n", group->id);
 
 	/* Pre-notify listeners that a device is being removed. */
 	blocking_notifier_call_chain(&group->notifier,
@@ -2337,8 +2337,8 @@ request_default_domain_for_dev(struct device *dev, unsigned long type)
 
 	iommu_group_create_direct_mappings(group, dev);
 
-	dev_info(dev, "Using iommu %s mapping\n",
-		 type == IOMMU_DOMAIN_DMA ? "dma" : "direct");
+	dev_dbg(dev, "Using iommu %s mapping\n",
+		type == IOMMU_DOMAIN_DMA ? "dma" : "direct");
 
 	ret = 0;
 out:
-- 
2.26.0.rc2

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Re: [PATCH] iommu: Lower severity of add/remove device messages

[Joerg Roedel]

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.

Regards,

	Joerg

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Re: [PATCH] iommu: Lower severity of add/remove device messages

[Ezequiel Garcia]

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 :-)

The idea is to reduce the amount of verbosity in the kernel.

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

Thanks!
Ezequiel

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Re: [PATCH] iommu: Lower severity of add/remove device messages

[Robin Murphy]

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?

Robin.
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Re: [PATCH] iommu: Lower severity of add/remove device messages

[Ezequiel Garcia]

On Fri, 2020-03-27 at 18:04 +0000, Robin Murphy wrote:
> 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?
> 

Do we really still have those???

Thanks,
Ezequiel

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