Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[kbuild test robot]

Hi Vivien,

[auto build test ERROR on net-next/master]

url:
https://github.com/0day-ci/linux/commits/Vivien-Didelot/net-dsa-tagger-simplification/20170531-032911
config: ia64-allmodconfig (attached as .config)
compiler: ia64-linux-gcc (GCC) 6.2.0
reproduce:
wget 
https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O 
~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=ia64 

All errors (new ones prefixed by >>):

   net/built-in.o: In function `eth_type_trans':
>> (.text+0xbf5f2): undefined reference to `dsa_uses_tagged_protocol'
   net/built-in.o: In function `ic_close_devs':
>> ipconfig.c:(.init.text+0x72c2): undefined reference to 
>> `dsa_uses_tagged_protocol'
   net/built-in.o: In function `ip_auto_config':
   ipconfig.c:(.init.text+0x8882): undefined reference to 
`dsa_uses_tagged_protocol'

---
0-DAY kernel test infrastructureOpen Source Technology Center
https://lists.01.org/pipermail/kbuild-all   Intel Corporation


.config.gz
Description: application/gzip

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[kbuild test robot]

Hi Vivien,

[auto build test ERROR on net-next/master]

url:
https://github.com/0day-ci/linux/commits/Vivien-Didelot/net-dsa-tagger-simplification/20170531-032911
config: ia64-allmodconfig (attached as .config)
compiler: ia64-linux-gcc (GCC) 6.2.0
reproduce:
wget 
https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O 
~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=ia64 

All errors (new ones prefixed by >>):

   net/built-in.o: In function `eth_type_trans':
>> (.text+0xbf5f2): undefined reference to `dsa_uses_tagged_protocol'
   net/built-in.o: In function `ic_close_devs':
>> ipconfig.c:(.init.text+0x72c2): undefined reference to 
>> `dsa_uses_tagged_protocol'
   net/built-in.o: In function `ip_auto_config':
   ipconfig.c:(.init.text+0x8882): undefined reference to 
`dsa_uses_tagged_protocol'

---
0-DAY kernel test infrastructureOpen Source Technology Center
https://lists.01.org/pipermail/kbuild-all   Intel Corporation


.config.gz
Description: application/gzip

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[Vivien Didelot]

Hi Andrew,

Andrew Lunn  writes:

> On Tue, May 30, 2017 at 11:56:30AM -0400, Vivien Didelot wrote:
>> Hi Andrew, David,
>> 
>> David Miller  writes:
>> 
>> >>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
>> >>> +{
>> >>> +return !!dst->rcv;
>> >>> +}
>> >>> +
>> >> 
>> >> You need to be careful here. This is in the hot path. Every frame
>> >> received uses this code. And think about a distro kernel, which might
>> >> have DSA enabled by default, yet is unlikely to have any switches. You
>> >> are adding a function call which can be called millions of times per
>> >> second
>> >
>> > Yeah, we really can't make this change.
>> >
>> > This isn't glibc where we're trying to hide the implementation of "FILE *"
>> > behind accessor functions that caller can't see.  We inline things when
>> > performance dictates, and it does here.
>> 
>> Thanks for the explanation, this wasn't obvious to me at all. So inline
>> is mandatory here. Would a dereference like "!!dst->tag_ops->rcv" have
>> an significant impact on performance?
>
> The additional dereference could cause a cache miss when accessing
> tag_ops, which is expensive. dst will be in cache, so dst->rcv should
> always be cheap.

OK! That was interesting. I'm dropping the first 2 patches.

Thanks,

Vivien

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[Vivien Didelot]

Hi Andrew,

Andrew Lunn  writes:

> On Tue, May 30, 2017 at 11:56:30AM -0400, Vivien Didelot wrote:
>> Hi Andrew, David,
>> 
>> David Miller  writes:
>> 
>> >>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
>> >>> +{
>> >>> +return !!dst->rcv;
>> >>> +}
>> >>> +
>> >> 
>> >> You need to be careful here. This is in the hot path. Every frame
>> >> received uses this code. And think about a distro kernel, which might
>> >> have DSA enabled by default, yet is unlikely to have any switches. You
>> >> are adding a function call which can be called millions of times per
>> >> second
>> >
>> > Yeah, we really can't make this change.
>> >
>> > This isn't glibc where we're trying to hide the implementation of "FILE *"
>> > behind accessor functions that caller can't see.  We inline things when
>> > performance dictates, and it does here.
>> 
>> Thanks for the explanation, this wasn't obvious to me at all. So inline
>> is mandatory here. Would a dereference like "!!dst->tag_ops->rcv" have
>> an significant impact on performance?
>
> The additional dereference could cause a cache miss when accessing
> tag_ops, which is expensive. dst will be in cache, so dst->rcv should
> always be cheap.

OK! That was interesting. I'm dropping the first 2 patches.

Thanks,

Vivien

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[Andrew Lunn]

On Tue, May 30, 2017 at 11:56:30AM -0400, Vivien Didelot wrote:
> Hi Andrew, David,
> 
> David Miller  writes:
> 
> >>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
> >>> +{
> >>> + return !!dst->rcv;
> >>> +}
> >>> +
> >> 
> >> You need to be careful here. This is in the hot path. Every frame
> >> received uses this code. And think about a distro kernel, which might
> >> have DSA enabled by default, yet is unlikely to have any switches. You
> >> are adding a function call which can be called millions of times per
> >> second
> >
> > Yeah, we really can't make this change.
> >
> > This isn't glibc where we're trying to hide the implementation of "FILE *"
> > behind accessor functions that caller can't see.  We inline things when
> > performance dictates, and it does here.
> 
> Thanks for the explanation, this wasn't obvious to me at all. So inline
> is mandatory here. Would a dereference like "!!dst->tag_ops->rcv" have
> an significant impact on performance?

The additional dereference could cause a cache miss when accessing
tag_ops, which is expensive. dst will be in cache, so dst->rcv should
always be cheap.

   Andrew

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[Andrew Lunn]

On Tue, May 30, 2017 at 11:56:30AM -0400, Vivien Didelot wrote:
> Hi Andrew, David,
> 
> David Miller  writes:
> 
> >>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
> >>> +{
> >>> + return !!dst->rcv;
> >>> +}
> >>> +
> >> 
> >> You need to be careful here. This is in the hot path. Every frame
> >> received uses this code. And think about a distro kernel, which might
> >> have DSA enabled by default, yet is unlikely to have any switches. You
> >> are adding a function call which can be called millions of times per
> >> second
> >
> > Yeah, we really can't make this change.
> >
> > This isn't glibc where we're trying to hide the implementation of "FILE *"
> > behind accessor functions that caller can't see.  We inline things when
> > performance dictates, and it does here.
> 
> Thanks for the explanation, this wasn't obvious to me at all. So inline
> is mandatory here. Would a dereference like "!!dst->tag_ops->rcv" have
> an significant impact on performance?

The additional dereference could cause a cache miss when accessing
tag_ops, which is expensive. dst will be in cache, so dst->rcv should
always be cheap.

   Andrew

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[Vivien Didelot]

Hi Andrew, David,

David Miller  writes:

>>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
>>> +{
>>> +   return !!dst->rcv;
>>> +}
>>> +
>> 
>> You need to be careful here. This is in the hot path. Every frame
>> received uses this code. And think about a distro kernel, which might
>> have DSA enabled by default, yet is unlikely to have any switches. You
>> are adding a function call which can be called millions of times per
>> second
>
> Yeah, we really can't make this change.
>
> This isn't glibc where we're trying to hide the implementation of "FILE *"
> behind accessor functions that caller can't see.  We inline things when
> performance dictates, and it does here.

Thanks for the explanation, this wasn't obvious to me at all. So inline
is mandatory here. Would a dereference like "!!dst->tag_ops->rcv" have
an significant impact on performance?

Thanks,

Vivien

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[Vivien Didelot]

Hi Andrew, David,

David Miller  writes:

>>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
>>> +{
>>> +   return !!dst->rcv;
>>> +}
>>> +
>> 
>> You need to be careful here. This is in the hot path. Every frame
>> received uses this code. And think about a distro kernel, which might
>> have DSA enabled by default, yet is unlikely to have any switches. You
>> are adding a function call which can be called millions of times per
>> second
>
> Yeah, we really can't make this change.
>
> This isn't glibc where we're trying to hide the implementation of "FILE *"
> behind accessor functions that caller can't see.  We inline things when
> performance dictates, and it does here.

Thanks for the explanation, this wasn't obvious to me at all. So inline
is mandatory here. Would a dereference like "!!dst->tag_ops->rcv" have
an significant impact on performance?

Thanks,

Vivien

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[David Miller]

From: Andrew Lunn 
Date: Tue, 30 May 2017 17:01:44 +0200

> On Tue, May 30, 2017 at 10:21:25AM -0400, Vivien Didelot wrote:
>> Hide the implementation of dsa_uses_tagged_protocol in dsa.c since this
>> helper will be extended to access the opaque dsa_device_ops structure.
>> 
>> At the same time, fix the checkpatch comparison check:
>> 
>> CHECK: Comparison to NULL could be written "dst->rcv"
>> #41: FILE: net/dsa/dsa.c:32:
>> +return dst->rcv != NULL;
>> 
>> Signed-off-by: Vivien Didelot 
>> ---
>>  include/net/dsa.h | 5 +
>>  net/dsa/dsa.c | 5 +
>>  2 files changed, 6 insertions(+), 4 deletions(-)
>> 
>> diff --git a/include/net/dsa.h b/include/net/dsa.h
>> index c0e567c0c824..cb5d668b265d 100644
>> --- a/include/net/dsa.h
>> +++ b/include/net/dsa.h
>> @@ -464,10 +464,7 @@ struct mii_bus *dsa_host_dev_to_mii_bus(struct device 
>> *dev);
>>  
>>  struct net_device *dsa_dev_to_net_device(struct device *dev);
>>  
>> -static inline bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
>> -{
>> -return dst->rcv != NULL;
>> -}
>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst);
>>  
>>  static inline bool netdev_uses_dsa(struct net_device *dev)
>>  {
>> diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
>> index 3288a80d4d6c..7a8a0358299b 100644
>> --- a/net/dsa/dsa.c
>> +++ b/net/dsa/dsa.c
>> @@ -27,6 +27,11 @@
>>  
>>  #include "dsa_priv.h"
>>  
>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
>> +{
>> +return !!dst->rcv;
>> +}
>> +
> 
> Hi Vivien
> 
> You need to be careful here. This is in the hot path. Every frame
> received uses this code. And think about a distro kernel, which might
> have DSA enabled by default, yet is unlikely to have any switches. You
> are adding a function call which can be called millions of times per
> second

Yeah, we really can't make this change.

This isn't glibc where we're trying to hide the implementation of "FILE *"
behind accessor functions that caller can't see.  We inline things when
performance dictates, and it does here.

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[David Miller]

From: Andrew Lunn 
Date: Tue, 30 May 2017 17:01:44 +0200

> On Tue, May 30, 2017 at 10:21:25AM -0400, Vivien Didelot wrote:
>> Hide the implementation of dsa_uses_tagged_protocol in dsa.c since this
>> helper will be extended to access the opaque dsa_device_ops structure.
>> 
>> At the same time, fix the checkpatch comparison check:
>> 
>> CHECK: Comparison to NULL could be written "dst->rcv"
>> #41: FILE: net/dsa/dsa.c:32:
>> +return dst->rcv != NULL;
>> 
>> Signed-off-by: Vivien Didelot 
>> ---
>>  include/net/dsa.h | 5 +
>>  net/dsa/dsa.c | 5 +
>>  2 files changed, 6 insertions(+), 4 deletions(-)
>> 
>> diff --git a/include/net/dsa.h b/include/net/dsa.h
>> index c0e567c0c824..cb5d668b265d 100644
>> --- a/include/net/dsa.h
>> +++ b/include/net/dsa.h
>> @@ -464,10 +464,7 @@ struct mii_bus *dsa_host_dev_to_mii_bus(struct device 
>> *dev);
>>  
>>  struct net_device *dsa_dev_to_net_device(struct device *dev);
>>  
>> -static inline bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
>> -{
>> -return dst->rcv != NULL;
>> -}
>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst);
>>  
>>  static inline bool netdev_uses_dsa(struct net_device *dev)
>>  {
>> diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
>> index 3288a80d4d6c..7a8a0358299b 100644
>> --- a/net/dsa/dsa.c
>> +++ b/net/dsa/dsa.c
>> @@ -27,6 +27,11 @@
>>  
>>  #include "dsa_priv.h"
>>  
>> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
>> +{
>> +return !!dst->rcv;
>> +}
>> +
> 
> Hi Vivien
> 
> You need to be careful here. This is in the hot path. Every frame
> received uses this code. And think about a distro kernel, which might
> have DSA enabled by default, yet is unlikely to have any switches. You
> are adding a function call which can be called millions of times per
> second

Yeah, we really can't make this change.

This isn't glibc where we're trying to hide the implementation of "FILE *"
behind accessor functions that caller can't see.  We inline things when
performance dictates, and it does here.

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[Andrew Lunn]

On Tue, May 30, 2017 at 10:21:25AM -0400, Vivien Didelot wrote:
> Hide the implementation of dsa_uses_tagged_protocol in dsa.c since this
> helper will be extended to access the opaque dsa_device_ops structure.
> 
> At the same time, fix the checkpatch comparison check:
> 
> CHECK: Comparison to NULL could be written "dst->rcv"
> #41: FILE: net/dsa/dsa.c:32:
> + return dst->rcv != NULL;
> 
> Signed-off-by: Vivien Didelot 
> ---
>  include/net/dsa.h | 5 +
>  net/dsa/dsa.c | 5 +
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index c0e567c0c824..cb5d668b265d 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -464,10 +464,7 @@ struct mii_bus *dsa_host_dev_to_mii_bus(struct device 
> *dev);
>  
>  struct net_device *dsa_dev_to_net_device(struct device *dev);
>  
> -static inline bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
> -{
> - return dst->rcv != NULL;
> -}
> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst);
>  
>  static inline bool netdev_uses_dsa(struct net_device *dev)
>  {
> diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
> index 3288a80d4d6c..7a8a0358299b 100644
> --- a/net/dsa/dsa.c
> +++ b/net/dsa/dsa.c
> @@ -27,6 +27,11 @@
>  
>  #include "dsa_priv.h"
>  
> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
> +{
> + return !!dst->rcv;
> +}
> +

Hi Vivien

You need to be careful here. This is in the hot path. Every frame
received uses this code. And think about a distro kernel, which might
have DSA enabled by default, yet is unlikely to have any switches. You
are adding a function call which can be called millions of times per
second

 Andrew

Re: [PATCH net-next 1/7] net: dsa: hide dsa_uses_tagged_protocol code

[Andrew Lunn]

On Tue, May 30, 2017 at 10:21:25AM -0400, Vivien Didelot wrote:
> Hide the implementation of dsa_uses_tagged_protocol in dsa.c since this
> helper will be extended to access the opaque dsa_device_ops structure.
> 
> At the same time, fix the checkpatch comparison check:
> 
> CHECK: Comparison to NULL could be written "dst->rcv"
> #41: FILE: net/dsa/dsa.c:32:
> + return dst->rcv != NULL;
> 
> Signed-off-by: Vivien Didelot 
> ---
>  include/net/dsa.h | 5 +
>  net/dsa/dsa.c | 5 +
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index c0e567c0c824..cb5d668b265d 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -464,10 +464,7 @@ struct mii_bus *dsa_host_dev_to_mii_bus(struct device 
> *dev);
>  
>  struct net_device *dsa_dev_to_net_device(struct device *dev);
>  
> -static inline bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
> -{
> - return dst->rcv != NULL;
> -}
> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst);
>  
>  static inline bool netdev_uses_dsa(struct net_device *dev)
>  {
> diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
> index 3288a80d4d6c..7a8a0358299b 100644
> --- a/net/dsa/dsa.c
> +++ b/net/dsa/dsa.c
> @@ -27,6 +27,11 @@
>  
>  #include "dsa_priv.h"
>  
> +bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
> +{
> + return !!dst->rcv;
> +}
> +

Hi Vivien

You need to be careful here. This is in the hot path. Every frame
received uses this code. And think about a distro kernel, which might
have DSA enabled by default, yet is unlikely to have any switches. You
are adding a function call which can be called millions of times per
second

 Andrew