Patchwork b44: properly use pr_fmt()

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Submitter Luis R. Rodriguez
Date April 24, 2012, 2:46 a.m.
Message ID <1335235603-32420-1-git-send-email-mcgrof@do-not-panic.com>
Download mbox | patch
Permalink /patch/154567/
State Changes Requested
Delegated to: David Miller
Headers show

Comments

Luis R. Rodriguez - April 24, 2012, 2:46 a.m.
From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>

pr_fmt() is either defined or we redefine it. Typically
drivers define it prior to including printk.h but this
is done under the assumption that no other subsystem
it uses has already defined pr_fmt(). In such cases
pr_fmt() should be undefined and redefined.

Doing this properly shaves down compilation time quite
considerably.

Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
---
 drivers/net/ethernet/broadcom/b44.c |    2 ++
 1 file changed, 2 insertions(+)
David Miller - April 24, 2012, 4:47 a.m.
From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
Date: Mon, 23 Apr 2012 19:46:43 -0700

> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
> 
> pr_fmt() is either defined or we redefine it. Typically
> drivers define it prior to including printk.h but this
> is done under the assumption that no other subsystem
> it uses has already defined pr_fmt(). In such cases
> pr_fmt() should be undefined and redefined.
> 
> Doing this properly shaves down compilation time quite
> considerably.
> 
> Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>

Every driver defines pr_fmt then includes the headers.  I do not
see any other place which performs the initial undef of pr_fmt
like you want to start doing here.

If there is a reason we should start doing this, it would appear
to be a universal reason, not one specific to this driver.  If
that's the case, we should formally agree to this and then work
on gradually converting all the drivers in reasonably sized chunks.

Either way I can't apply this patch as-is, sorry Luis.
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Luis R. Rodriguez - April 26, 2012, 12:23 p.m.
On Mon, Apr 23, 2012 at 9:47 PM, David Miller <davem@davemloft.net> wrote:
> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
> Date: Mon, 23 Apr 2012 19:46:43 -0700
>
>> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
>>
>> pr_fmt() is either defined or we redefine it. Typically
>> drivers define it prior to including printk.h but this
>> is done under the assumption that no other subsystem
>> it uses has already defined pr_fmt(). In such cases
>> pr_fmt() should be undefined and redefined.
>>
>> Doing this properly shaves down compilation time quite
>> considerably.
>>
>> Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
>
> Every driver defines pr_fmt then includes the headers.  I do not
> see any other place which performs the initial undef of pr_fmt
> like you want to start doing here.

One example is, and that is where I got the hint:

drivers/net/wireless/mwifiex/decl.h

> If there is a reason we should start doing this, it would appear
> to be a universal reason, not one specific to this driver.

Sure.

> If that's the case, we should formally agree to this and then work
> on gradually converting all the drivers in reasonably sized chunks.

Understood.

> Either way I can't apply this patch as-is, sorry Luis.

So the issue can occur if any parent header ends up defining this,
this could happen if a subsystem wants to define the pr_fmt in their
own header and a driver for example wants to override this. In theory
this does not occur but in practice this may vary and if we want to
ensure this does not happen perhaps the thing to do is to document
this as such.

I just tested allmodconfig though and checked compilation for V=1
against drivers/net/wireless/ and found no issues against linux-next
though so in practice at least for wireless networking it seems we are
squeaky clean in its usage. I'll test across the kernel though next to
see if there are any real violators of the assumption. Unfortunately
I've hit an issue with compiling allmodconfig already with linux-next
that is already reported so my homework will be to find a shiny
linux-next to compile test against allmodconfig.

An area that this does clearly happen but that likely does not merit
and upstream change for is in the backport work compat that defines
this for older kernels and later we have to also backport users of
pr_fmt such as pr_emerg_once. Ultimately drivers will want to actually
then override this and in that case the undef is necessary as
otherwise you get the redefinition warning which incurs in practice a
considerable CPU performance hit at compilation time.

  Luis
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Luis R. Rodriguez - April 26, 2012, 1:02 p.m.
On Thu, Apr 26, 2012 at 5:23 AM, Luis R. Rodriguez
<mcgrof@do-not-panic.com> wrote:
> On Mon, Apr 23, 2012 at 9:47 PM, David Miller <davem@davemloft.net> wrote:
>> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
>> Date: Mon, 23 Apr 2012 19:46:43 -0700
>>
>>> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
>>>
>>> pr_fmt() is either defined or we redefine it. Typically
>>> drivers define it prior to including printk.h but this
>>> is done under the assumption that no other subsystem
>>> it uses has already defined pr_fmt(). In such cases
>>> pr_fmt() should be undefined and redefined.
>>>
>>> Doing this properly shaves down compilation time quite
>>> considerably.
>>>
>>> Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
>>
>> Every driver defines pr_fmt then includes the headers.  I do not
>> see any other place which performs the initial undef of pr_fmt
>> like you want to start doing here.
>
> One example is, and that is where I got the hint:
>
> drivers/net/wireless/mwifiex/decl.h
>
>> If there is a reason we should start doing this, it would appear
>> to be a universal reason, not one specific to this driver.
>
> Sure.
>
>> If that's the case, we should formally agree to this and then work
>> on gradually converting all the drivers in reasonably sized chunks.
>
> Understood.
>
>> Either way I can't apply this patch as-is, sorry Luis.
>
> So the issue can occur if any parent header ends up defining this,
> this could happen if a subsystem wants to define the pr_fmt in their
> own header and a driver for example wants to override this. In theory
> this does not occur but in practice this may vary and if we want to
> ensure this does not happen perhaps the thing to do is to document
> this as such.
>
> I just tested allmodconfig though and checked compilation for V=1
> against drivers/net/wireless/ and found no issues against linux-next
> though so in practice at least for wireless networking it seems we are
> squeaky clean in its usage. I'll test across the kernel though next to
> see if there are any real violators of the assumption. Unfortunately
> I've hit an issue with compiling allmodconfig already with linux-next
> that is already reported so my homework will be to find a shiny
> linux-next to compile test against allmodconfig.
>
> An area that this does clearly happen but that likely does not merit
> and upstream change for is in the backport work compat that defines
> this for older kernels and later we have to also backport users of
> pr_fmt such as pr_emerg_once. Ultimately drivers will want to actually
> then override this and in that case the undef is necessary as
> otherwise you get the redefinition warning which incurs in practice a
> considerable CPU performance hit at compilation time.

Additionally Arend has pointed pointed out that previously printk.h
was removed as a direct include as well given that kernel.h includes
it already:

https://lkml.org/lkml/2011/5/25/331

So this would be a second issue with this patch.

  Luis
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Luis R. Rodriguez - April 26, 2012, 3:53 p.m.
On Thu, Apr 26, 2012 at 6:02 AM, Luis R. Rodriguez
<mcgrof@do-not-panic.com> wrote:
> On Thu, Apr 26, 2012 at 5:23 AM, Luis R. Rodriguez
> <mcgrof@do-not-panic.com> wrote:
>> On Mon, Apr 23, 2012 at 9:47 PM, David Miller <davem@davemloft.net> wrote:
>>> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
>>> Date: Mon, 23 Apr 2012 19:46:43 -0700
>>>
>>>> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
>>>>
>>>> pr_fmt() is either defined or we redefine it. Typically
>>>> drivers define it prior to including printk.h but this
>>>> is done under the assumption that no other subsystem
>>>> it uses has already defined pr_fmt(). In such cases
>>>> pr_fmt() should be undefined and redefined.
>>>>
>>>> Doing this properly shaves down compilation time quite
>>>> considerably.
>>>>
>>>> Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
>>>
>>> Every driver defines pr_fmt then includes the headers.  I do not
>>> see any other place which performs the initial undef of pr_fmt
>>> like you want to start doing here.
>>
>> One example is, and that is where I got the hint:
>>
>> drivers/net/wireless/mwifiex/decl.h
>>
>>> If there is a reason we should start doing this, it would appear
>>> to be a universal reason, not one specific to this driver.
>>
>> Sure.
>>
>>> If that's the case, we should formally agree to this and then work
>>> on gradually converting all the drivers in reasonably sized chunks.
>>
>> Understood.
>>
>>> Either way I can't apply this patch as-is, sorry Luis.
>>
>> So the issue can occur if any parent header ends up defining this,
>> this could happen if a subsystem wants to define the pr_fmt in their
>> own header and a driver for example wants to override this. In theory
>> this does not occur but in practice this may vary and if we want to
>> ensure this does not happen perhaps the thing to do is to document
>> this as such.
>>
>> I just tested allmodconfig though and checked compilation for V=1
>> against drivers/net/wireless/ and found no issues against linux-next
>> though so in practice at least for wireless networking it seems we are
>> squeaky clean in its usage. I'll test across the kernel though next to
>> see if there are any real violators of the assumption. Unfortunately
>> I've hit an issue with compiling allmodconfig already with linux-next
>> that is already reported so my homework will be to find a shiny
>> linux-next to compile test against allmodconfig.
>>
>> An area that this does clearly happen but that likely does not merit
>> and upstream change for is in the backport work compat that defines
>> this for older kernels and later we have to also backport users of
>> pr_fmt such as pr_emerg_once. Ultimately drivers will want to actually
>> then override this and in that case the undef is necessary as
>> otherwise you get the redefinition warning which incurs in practice a
>> considerable CPU performance hit at compilation time.
>
> Additionally Arend has pointed pointed out that previously printk.h
> was removed as a direct include as well given that kernel.h includes
> it already:
>
> https://lkml.org/lkml/2011/5/25/331
>
> So this would be a second issue with this patch.

OK I found no pr_fmt warnings at all for make allmodconfig ; make V=1
; on v3.4-rc4. For this and others reason stated then yes, this patch
is simply bogus.

  Luis
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David Miller - April 26, 2012, 8:07 p.m.
From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
Date: Thu, 26 Apr 2012 08:53:30 -0700

> OK I found no pr_fmt warnings at all for make allmodconfig ; make V=1
> ; on v3.4-rc4. For this and others reason stated then yes, this patch
> is simply bogus.

This is what I expected, thanks for sorting this out :-)

We're in the rally!
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Luis R. Rodriguez - April 26, 2012, 8:30 p.m.
On Thu, Apr 26, 2012 at 1:07 PM, David Miller <davem@davemloft.net> wrote:
> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
> Date: Thu, 26 Apr 2012 08:53:30 -0700
>
>> OK I found no pr_fmt warnings at all for make allmodconfig ; make V=1
>> ; on v3.4-rc4. For this and others reason stated then yes, this patch
>> is simply bogus.
>
> This is what I expected, thanks for sorting this out :-)

Thanks for kicking me in the balls.

> We're in the rally!

This is the highlight of my life (8:17) !

  Luis
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Patch

diff --git a/drivers/net/ethernet/broadcom/b44.c b/drivers/net/ethernet/broadcom/b44.c
index 46b8b7d..656f323 100644
--- a/drivers/net/ethernet/broadcom/b44.c
+++ b/drivers/net/ethernet/broadcom/b44.c
@@ -10,9 +10,11 @@ 
  * Distribute under GPL.
  */
 
+#undef pr_fmt
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/kernel.h>
+#include <linux/printk.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/types.h>