Re: [dpdk-dev] [PATCH] eal: fix lcore state bug

[Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>]

Hi Phil,

W dniu 29.04.2020 o 17:07, Phil Yang pisze:
> Hi Lukasz,
>
>> -----Original Message-----
>> From: dev <dev-bounces@dpdk.org> On Behalf Of Lukasz Wojciechowski
>> Sent: Tuesday, April 28, 2020 9:22 AM
>> To: Harry van Haaren <harry.van.haaren@intel.com>; Jerin Jacob
>> <jerin.jacob@caviumnetworks.com>
>> Cc: dev@dpdk.org; l.wojciechow@partner.samsung.com; stable@dpdk.org
>> Subject: [dpdk-dev] [PATCH] eal: fix lcore state bug
>>
>> The rte_service_lcore_reset_all function stops execution of services
>> on all lcores and switches them back from ROLE_SERVICE to ROLE_RTE.
>> However the thread loop for slave lcores (eal_thread_loop) distincts these
>> roles to set lcore state after processing delegated function.
>> It sets WAIT state for ROLE_SERVICE, but FINISHED for ROLE_RTE.
>> So changing the role to RTE before stopping work in slave lcores
>> causes lcores to end in FINISHED state. That is why the rte_eal_lcore_wait
>> must be run after rte_service_lcore_reset_all to bring back lcores to
>> launchable (WAIT) state.
> Is that make sense to call rte_eal_mp_wait_lcore() inside rte_serice_lcore_reset_all() ?

yeah, I thought about it and in my opinion the answer is no, because if 
the function run on slave lcore is in FINISHED state it means, that 
someone can still read the value returned by the function and the only 
one who can be interested in the value is the one that delegated the 
service.

If we will wait for lcores to end their jobs, read the values and switch 
them to WAIT state, the values will be lost. The application might need 
to read them. We cannot take this possibility from it.

> <snip>
>
> Thanks,
> Phil

-- 

Lukasz Wojciechowski
Principal Software Engineer

Samsung R&D Institute Poland
Samsung Electronics
Office +48 22 377 88 25
l.wojciechow@partner.samsung.com