Re: [dpdk-dev] [PATCH] rte_flow: mark rte_flow_error_set as cold

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 5/21/2019 3:31 PM, Stephen Hemminger wrote:
> On Tue, 21 May 2019 08:01:53 +0000
> "Van Haaren, Harry" <harry.van.haaren@intel.com> wrote:
> 
>>> -----Original Message-----
>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen Hemminger
>>> Sent: Monday, May 20, 2019 11:52 PM
>>> To: adrien.mazarguil@6wind.com
>>> Cc: dev@dpdk.org; Stephen Hemminger <stephen@networkplumber.org>
>>> Subject: [dpdk-dev] [PATCH] rte_flow: mark rte_flow_error_set as cold
>>>
>>> A minor optimization that save a few cycles during flow setup.
>>>
>>> Use the GCC cold attribute for the rte_flow_error_set function.
>>> This attribute implicitly marks all code paths that arrive at
>>> this function as unlikely.  
>>
>> Interesting - wasn't aware this is what the "cold" attribute does.
>>
>>
>>>  lib/librte_ethdev/rte_flow.h | 8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/lib/librte_ethdev/rte_flow.h b/lib/librte_ethdev/rte_flow.h
>>> index 63f84fca65c4..dc821be43f19 100644
>>> --- a/lib/librte_ethdev/rte_flow.h
>>> +++ b/lib/librte_ethdev/rte_flow.h
>>> @@ -2591,7 +2591,13 @@ rte_flow_error_set(struct rte_flow_error *error,
>>>  		   int code,
>>>  		   enum rte_flow_error_type type,
>>>  		   const void *cause,
>>> -		   const char *message);
>>> +		   const char *message)
>>> +#ifdef __GNUC__
>>> +#if (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 2))
>>> +	__attribute__((cold))
>>> +#endif
>>> +#endif
>>> +	;  
>>
>>
>> Would it be worth making an  __rte_attribute_cold  or similar?
>> Less in-place #ifdefs and there are probably other locations in
>> DPDK that would also benefit from such an annotation.

+1 to define '__rte_cold' [1] in 'lib/librte_eal/common/include/rte_common.h'
as defined other similar compiler attributes there.

[1]
or '__rte_attribute_cold' but all other attribute defines are missing
'attribute' keyword, so I think can be skipped here as well

>>
>> -Harry
> 
> I just cloned what was already on rte_log.
>