Re: [dpdk-dev] [PATCH 1/2] ethdev: make flow API primary/secondary process safe

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

On 4/15/2021 3:55 AM, Suanming Mou wrote:
> Hi,
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>> Sent: Wednesday, April 14, 2021 9:07 PM
>> To: Suanming Mou <suanmingm@nvidia.com>; Ori Kam <orika@nvidia.com>;
>> Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>; NBU-Contact-Thomas
>> Monjalon <thomas@monjalon.net>
>> Cc: dev@dpdk.org; Stephen Hemminger <stephen@networkplumber.org>
>> Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: make flow API primary/secondary
>> process safe
>>
>> On 3/16/2021 11:48 PM, Suanming Mou wrote:
>>> Hi Stephen,
>>>
>>>> -----Original Message-----
>>>> From: Stephen Hemminger <stephen@networkplumber.org>
>>>> Sent: Tuesday, March 16, 2021 3:27 AM
>>>> To: dev@dpdk.org
>>>> Cc: Stephen Hemminger <stephen@networkplumber.org>; Suanming Mou
>>>> <suanmingm@nvidia.com>
>>>> Subject: [PATCH 1/2] ethdev: make flow API primary/secondary process
>>>> safe
>>>>
>>>> Posix mutex are not by default safe for protecting for usage from
>>>> multiple processes. The flow ops mutex could be used by both primary
>>>> and secondary processes.
>>>
>>> Process safe is something more widely scope. I assume it should be another
>> feature but not a bugfix for thread-safe?
>>> And the fag RTE_ETH_DEV_FLOW_OPS_THREAD_SAFE we have added is just
>> thread safe.
>>>
>>
>> Hi Suanming,
>>
>> I think 'RTE_ETH_DEV_FLOW_OPS_THREAD_SAFE' flag and what this patch
>> address are different issues.
>>
>> 'RTE_ETH_DEV_FLOW_OPS_THREAD_SAFE' is to add/remove synchronization
>> support for flow APIs, that is for thread safety as flag name suggests.
>>
>> This patch is to solve the problem for multi process, where commit log describes
>> as posix mutex is not safe for multiple process.
> 
> So for PMDs which not set the RTE_ETH_DEV_FLOW_OPS_THREAD_SAFE capability bit, they will have the process level protection in multi-process.
> For PMDs which set the RTE_ETH_DEV_FLOW_OPS_THREAD_SAFE capability bit, this change does not help with these PMDs. If the PMD with RTE_ETH_DEV_FLOW_OPS_THREAD_SAFE capability bit  internally does not support multi-process, they may still suffer crash etc.

Correct

> (If I understand correctly, mlx PMD level now should support multi-process, but better to have the confirmation from maintainers with much deeper level).
> I assume this patch solves the posix mutex for multi-process only, hard to say the flow API primary/secondary process safe after that patch.
> 

I am also not quite sure how PMDs that doesn't require mutex at all, (mlx5, 
bnxt, sfc) behave on multi process. Is calling flow APIs from both 
primary/secondary safe?

>>
>>
>> Stephen,
>> Are you aware of any downside setting 'PTHREAD_PROCESS_SHARED' attribute
>> to the
>> mutex? Any possible performance implications?
>>
>> Ori,
>> Since mlx is heavily using the flow API, is it possible to test this patch? If
>> there is no negative impact, I think we can get this patch, what do you think?
>>
>>>>
>>>> Bugzilla ID: 662
>>>> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
>>>> Fixes: 80d1a9aff7f6 ("ethdev: make flow API thread safe")
>>>> Cc: suanmingm@nvidia.com
>>>> ---
>>>>    lib/librte_ethdev/rte_ethdev.c | 6 +++++-
>>>>    1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
>> index
>>>> 6f514c388b4e..d1024df408a5 100644
>>>> --- a/lib/librte_ethdev/rte_ethdev.c
>>>> +++ b/lib/librte_ethdev/rte_ethdev.c
>>>> @@ -470,6 +470,7 @@ rte_eth_dev_allocate(const char *name)  {
>>>>    	uint16_t port_id;
>>>>    	struct rte_eth_dev *eth_dev = NULL;
>>>> +	pthread_mutexattr_t attr;
>>>>    	size_t name_len;
>>>>
>>>>    	name_len = strnlen(name, RTE_ETH_NAME_MAX_LEN); @@ -506,7
>>>> +507,10 @@ rte_eth_dev_allocate(const char *name)
>>>>    	strlcpy(eth_dev->data->name, name, sizeof(eth_dev->data->name));
>>>>    	eth_dev->data->port_id = port_id;
>>>>    	eth_dev->data->mtu = RTE_ETHER_MTU;
>>>> -	pthread_mutex_init(&eth_dev->data->flow_ops_mutex, NULL);
>>>> +
>>>> +	pthread_mutexattr_init(&attr);
>>>> +	pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
>>>>
>>>> +	pthread_mutex_init(&eth_dev->data->flow_ops_mutex, &attr);
>>>>
>>>>    unlock:
>>>>    	rte_spinlock_unlock(&eth_dev_shared_data->ownership_lock);
>>>> --
>>>> 2.30.2
>>>
>