[dpdk-dev] [PATCH 2/2] lpm: hide internal data

[Medvedkin, Vladimir]

Hi Michel,

Could you please describe a condition when LPM gets inconsistent? As I 
can see if there is no free tbl8 it will return -ENOSPC.

On 13/10/2020 15:58, Michel Machado wrote:
> Hi Kevin,
> 
>     We do need fields max_rules and number_tbl8s of struct rte_lpm, so 
> the removal would force us to have another patch to our local copy of 
> DPDK. We'd rather avoid this new local patch because we wish to 
> eventually be in sync with the stock DPDK.
> 
>     Those fields are needed in Gatekeeper because we found a condition 
> in an ongoing deployment in which the entries of some LPM tables may 
> suddenly change a lot to reflect policy changes. To avoid getting into a 
> state in which the LPM table is inconsistent because it cannot fit all 
> the new entries, we compute the needed parameters to support the new 
> entries, and compare with the current parameters. If the current table 
> doesn't fit everything, we have to replace it with a new LPM table.
> 
>     If there were a way to obtain the struct rte_lpm_config of a given 
> LPM table, it would cleanly address our need. We have the same need in 
> IPv6 and have a local patch to work around it (see 
> https://github.com/cjdoucette/dpdk/commit/3eaf124a781349b8ec8cd880db26a78115cb8c8f). 
> Thus, an IPv4 and IPv6 solution would be best.
> 
>     PS: I've added Qiaobin Fu, another Gatekeeper maintainer, to this 
> disscussion.
> 
> [ ]'s
> Michel Machado
> 
> On 10/13/20 9:53 AM, Kevin Traynor wrote:
>> Hi Gatekeeper maintainers (I think),
>>
>> fyi - there is a proposal to remove some members of a struct in DPDK LPM
>> API that Gatekeeper is using [1]. It would be only from DPDK 20.11 but
>> as it's an LTS I guess it would probably hit Debian in a few months.
>>
>> The full thread is here:
>> http://inbox.dpdk.org/dev/20200907081518.46350-1-ruifeng.wang@arm.com/
>>
>> Maybe you can take a look and tell us if they are needed in Gatekeeper
>> or you can workaround it?
>>
>> thanks,
>> Kevin.
>>
>> [1]
>> https://github.com/AltraMayor/gatekeeper/blob/master/gt/lua_lpm.c#L235-L248 
>>
>>
>> On 09/10/2020 07:54, Ruifeng Wang wrote:
>>>
>>>> -----Original Message-----
>>>> From: Kevin Traynor <ktraynor at redhat.com>
>>>> Sent: Wednesday, September 30, 2020 4:46 PM
>>>> To: Ruifeng Wang <Ruifeng.Wang at arm.com>; Medvedkin, Vladimir
>>>> <vladimir.medvedkin at intel.com>; Bruce Richardson
>>>> <bruce.richardson at intel.com>
>>>> Cc: dev at dpdk.org; Honnappa Nagarahalli
>>>> <Honnappa.Nagarahalli at arm.com>; nd <nd at arm.com>
>>>> Subject: Re: [dpdk-dev] [PATCH 2/2] lpm: hide internal data
>>>>
>>>> On 16/09/2020 04:17, Ruifeng Wang wrote:
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Medvedkin, Vladimir <vladimir.medvedkin at intel.com>
>>>>>> Sent: Wednesday, September 16, 2020 12:28 AM
>>>>>> To: Bruce Richardson <bruce.richardson at intel.com>; Ruifeng Wang
>>>>>> <Ruifeng.Wang at arm.com>
>>>>>> Cc: dev at dpdk.org; Honnappa Nagarahalli
>>>>>> <Honnappa.Nagarahalli at arm.com>; nd <nd at arm.com>
>>>>>> Subject: Re: [PATCH 2/2] lpm: hide internal data
>>>>>>
>>>>>> Hi Ruifeng,
>>>>>>
>>>>>> On 15/09/2020 17:02, Bruce Richardson wrote:
>>>>>>> On Mon, Sep 07, 2020 at 04:15:17PM +0800, Ruifeng Wang wrote:
>>>>>>>> Fields except tbl24 and tbl8 in rte_lpm structure have no need to
>>>>>>>> be exposed to the user.
>>>>>>>> Hide the unneeded exposure of structure fields for better ABI
>>>>>>>> maintainability.
>>>>>>>>
>>>>>>>> Suggested-by: David Marchand <david.marchand at redhat.com>
>>>>>>>> Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
>>>>>>>> Reviewed-by: Phil Yang <phil.yang at arm.com>
>>>>>>>> ---
>>>>>>>>    lib/librte_lpm/rte_lpm.c | 152
>>>>>>>> +++++++++++++++++++++++---------------
>>>>>> -
>>>>>>>>    lib/librte_lpm/rte_lpm.h |   7 --
>>>>>>>>    2 files changed, 91 insertions(+), 68 deletions(-)
>>>>>>>>
>>>>>>> <snip>
>>>>>>>> diff --git a/lib/librte_lpm/rte_lpm.h b/lib/librte_lpm/rte_lpm.h
>>>>>>>> index 03da2d37e..112d96f37 100644
>>>>>>>> --- a/lib/librte_lpm/rte_lpm.h
>>>>>>>> +++ b/lib/librte_lpm/rte_lpm.h
>>>>>>>> @@ -132,17 +132,10 @@ struct rte_lpm_rule_info {
>>>>>>>>
>>>>>>>>    /** @internal LPM structure. */
>>>>>>>>    struct rte_lpm {
>>>>>>>> -    /* LPM metadata. */
>>>>>>>> -    char name[RTE_LPM_NAMESIZE];        /**< Name of the lpm. */
>>>>>>>> -    uint32_t max_rules; /**< Max. balanced rules per lpm. */
>>>>>>>> -    uint32_t number_tbl8s; /**< Number of tbl8s. */
>>>>>>>> -    struct rte_lpm_rule_info rule_info[RTE_LPM_MAX_DEPTH]; /**<
>>>>>> Rule info table. */
>>>>>>>> -
>>>>>>>>        /* LPM Tables. */
>>>>>>>>        struct rte_lpm_tbl_entry tbl24[RTE_LPM_TBL24_NUM_ENTRIES]
>>>>>>>>                __rte_cache_aligned; /**< LPM tbl24 table. */
>>>>>>>>        struct rte_lpm_tbl_entry *tbl8; /**< LPM tbl8 table. */
>>>>>>>> -    struct rte_lpm_rule *rules_tbl; /**< LPM rules. */
>>>>>>>>    };
>>>>>>>>
>>>>>>>
>>>>>>> Since this changes the ABI, does it not need advance notice?
>>>>>>>
>>>>>>> [Basically the return value point from rte_lpm_create() will be
>>>>>>> different, and that return value could be used by rte_lpm_lookup()
>>>>>>> which as a static inline function will be in the binary and using
>>>>>>> the old structure offsets.]
>>>>>>>
>>>>>>
>>>>>> Agree with Bruce, this patch breaks ABI, so it can't be accepted
>>>>>> without prior notice.
>>>>>>
>>>>> So if the change wants to happen in 20.11, a deprecation notice should
>>>>> have been added in 20.08.
>>>>> I should have added a deprecation notice. This change will have to 
>>>>> wait for
>>>> next ABI update window.
>>>>>
>>>>
>>>> Do you plan to extend? or is this just speculative?
>>> It is speculative.
>>>
>>>>
>>>> A quick scan and there seems to be several projects using some of these
>>>> members that you are proposing to hide. e.g. BESS, NFF-Go, DPVS,
>>>> gatekeeper. I didn't look at the details to see if they are really 
>>>> needed.
>>>>
>>>> Not sure how much notice they'd need or if they update DPDK much, but I
>>>> think it's worth having a closer look as to how they use lpm and 
>>>> what the
>>>> impact to them is.
>>> Checked the projects listed above. BESS, NFF-Go and DPVS don't access 
>>> the members to be hided.
>>> They will not be impacted by this patch.
>>> But Gatekeeper accesses the rte_lpm internal members that to be 
>>> hided. Its compilation will be broken with this patch.
>>>
>>>>
>>>>> Thanks.
>>>>> Ruifeng
>>>>>>>>    /** LPM RCU QSBR configuration structure. */
>>>>>>>> -- 
>>>>>>>> 2.17.1
>>>>>>>>
>>>>>>
>>>>>> -- 
>>>>>> Regards,
>>>>>> Vladimir
>>>
>>

-- 
Regards,
Vladimir