[PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[Joakim Hernberg]

Since the HWLAT_DETECTOR driver supposedly shouldn't be builtin, but a
module when used at all, it would make sense to limit the configuration
choices:

Signed-off-by: Joakim Hernberg <jhernberg@alchemy.lu>
Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

---
 drivers/misc/Kconfig | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 453a616..94756c3 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -124,8 +124,7 @@ config IBM_ASM
 
 config HWLAT_DETECTOR
 	tristate "Testing module to detect hardware-induced latencies"
-	depends on DEBUG_FS
-	depends on RING_BUFFER
+	depends on DEBUG_FS && RING_BUFFER && m
 	default m
 	---help---
 	  A simple hardware latency detector. Use this module to detect
-- 
2.5.3

-- 

   Joakim
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Re: [PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[Sebastian Andrzej Siewior]

* Joakim Hernberg | 2015-09-23 19:33:40 [+0200]:

>Since the HWLAT_DETECTOR driver supposedly shouldn't be builtin, but a
>module when used at all, it would make sense to limit the configuration
>choices:

what is wrong with it beeing built-in? The default is m already.

>Signed-off-by: Joakim Hernberg <jhernberg@alchemy.lu>
>Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Sebastian
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Re: [PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[Joakim Hernberg]

On Fri, 11 Dec 2015 17:52:40 +0100
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> * Joakim Hernberg | 2015-09-23 19:33:40 [+0200]:
> 
> >Since the HWLAT_DETECTOR driver supposedly shouldn't be builtin, but
> >a module when used at all, it would make sense to limit the
> >configuration choices:  
> 
> what is wrong with it beeing built-in? The default is m already.

To be quite honest I'm not quite sure anymore, think it fails when
built in.  I also faintly remember an irc discussion where it was
claimed that it shouldn't be built into the kernel, think that was the
reason for creating the patch.

-- 

   Joakim

Re: [PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[Joakim Hernberg]

On Fri, 11 Dec 2015 17:52:40 +0100
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> * Joakim Hernberg | 2015-09-23 19:33:40 [+0200]:
> 
> >Since the HWLAT_DETECTOR driver supposedly shouldn't be builtin, but
> >a module when used at all, it would make sense to limit the
> >configuration choices:  
> 
> what is wrong with it beeing built-in? The default is m already.
> 
> >Signed-off-by: Joakim Hernberg <jhernberg@alchemy.lu>
> >Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>  
> 
> Sebastian

I looked at the IRC logs from when this was discussed.  The hwlatdetect
script looks for the kernel module and will fail if it's built-in (or
compressed).  Also this quote from irc: <jkacur> I need to look
at the code, but offhand, I think we said, it cannot be a built-in by design

These were the reasons for the patch.

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   Joakim
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Re: [PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[Sebastian Andrzej Siewior]

* Joakim Hernberg | 2015-12-13 11:39:35 [+0100]:

>I looked at the IRC logs from when this was discussed.  The hwlatdetect
>script looks for the kernel module and will fail if it's built-in (or
>compressed).  Also this quote from irc: <jkacur> I need to look
>at the code, but offhand, I think we said, it cannot be a built-in by design

Why can't it work by design in built-in mode? The module parameters
`enabled` and `threshold` can be set via debugfs (and via command line).
So I don't see here the difference between module and built-in.
Is there something I missed?

If the hwlatdetect script is not able to handle that then it deserves to
be fixed. The same goes for support of compressed modules.

>These were the reasons for the patch.

Sebastian

Re: [PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[John Kacur]

----- Original Message -----
> * Joakim Hernberg | 2015-12-13 11:39:35 [+0100]:
> 
> >I looked at the IRC logs from when this was discussed.  The hwlatdetect
> >script looks for the kernel module and will fail if it's built-in (or
> >compressed).  Also this quote from irc: <jkacur> I need to look
> >at the code, but offhand, I think we said, it cannot be a built-in by design
> 
> Why can't it work by design in built-in mode? The module parameters
> `enabled` and `threshold` can be set via debugfs (and via command line).
> So I don't see here the difference between module and built-in.
> Is there something I missed?
> 
> If the hwlatdetect script is not able to handle that then it deserves to
> be fixed. The same goes for support of compressed modules.
> 
> >These were the reasons for the patch.
> 

The script can be made to handle it, that's not a big deal. I think the historical
reason was worrying that people could be accidentally running a kernel with
some really heavy weight debugging that would affect performance. However, let people
hang themselves if they want. Clark was going to send a patch to allow it, but probably
ran out of time before the holidays. You can beat him to the punch if you want, or wait
for him.

John

Re: [PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[Sebastian Andrzej Siewior]

On 12/22/2015 05:25 PM, John Kacur wrote:
> The script can be made to handle it, that's not a big deal. I think the historical
> reason was worrying that people could be accidentally running a kernel with
> some really heavy weight debugging that would affect performance. However, let people
> hang themselves if they want.

How can people hang themselves if they build it *into* the kernel? If I
understand *how* this can happen I will try to address it. However from
what I can see right now, nothing will happen if this module is built
into the kernel.

> 
> John
> 
Sebastian

Re: [PATCH] make HWLAT_DETECTOR kernel config either disabled or a module, never builtin.

[John Kacur]

----- Original Message -----
> On 12/22/2015 05:25 PM, John Kacur wrote:
> > The script can be made to handle it, that's not a big deal. I think the
> > historical
> > reason was worrying that people could be accidentally running a kernel with
> > some really heavy weight debugging that would affect performance. However,
> > let people
> > hang themselves if they want.
> 
> How can people hang themselves if they build it *into* the kernel? If I
> understand *how* this can happen I will try to address it. However from
> what I can see right now, nothing will happen if this module is built
> into the kernel.
> 
> > 
> > John
> > 
> Sebastian

All I mean is if you are accidentally running a debug kernel, you're going
to get really bad performance, which is obvious. However, why are you arguing
with me, I'm agreeing with and Clark is agreeing with you, let's make it possible
for people to enable it now, and forget whatever historical reason stopped us from
doing that before.

John