[dpdk-dev] [PATCH] eal: add option --avail-cores to detect lcores

[Tan, Jianfeng]

On 3/9/2016 10:01 PM, Ananyev, Konstantin wrote:
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Tan, Jianfeng
>> Sent: Wednesday, March 09, 2016 1:53 PM
>> To: Panu Matilainen; dev at dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH] eal: add option --avail-cores to detect lcores
>>
>>
>>
>> On 3/9/2016 9:05 PM, Panu Matilainen wrote:
>>> On 03/08/2016 07:38 PM, Tan, Jianfeng wrote:
>>>> Hi Panu,
>>>>
>>>> On 3/8/2016 4:54 PM, Panu Matilainen wrote:
>>>>> On 03/04/2016 12:05 PM, Jianfeng Tan wrote:
>>>>>> This patch adds option, --avail-cores, to use lcores which are
>>>>>> available
>>>>>> by calling pthread_getaffinity_np() to narrow down detected cores
>>>>>> before
>>>>>> parsing coremask (-c), corelist (-l), and coremap (--lcores).
>>>>>>
>>>>>> Test example:
>>>>>> $ taskset 0xc0000 ./examples/helloworld/build/helloworld \
>>>>>>          --avail-cores -m 1024
>>>>>>
>>>>>> Signed-off-by: Jianfeng Tan <jianfeng.tan at intel.com>
>>>>>> Acked-by: Neil Horman <nhorman at tuxdriver.com>
>>>>> Hmm, to me this sounds like something that should be done always so
>>>>> there's no need for an option. Or if there's a chance it might do the
>>>>> wrong thing in some rare circumstance then perhaps there should be a
>>>>> disabler option instead?
>>>> Thanks for comments.
>>>>
>>>> Yes, there's a use case that we cannot handle.
>>>>
>>>> If we make it as default, DPDK applications may fail to start, when user
>>>> specifies a core in isolcpus and its parent process (say bash) has a
>>>> cpuset affinity that excludes isolcpus. Originally, DPDK applications
>>>> just blindly do pthread_setaffinity_np() and it always succeeds because
>>>> it always has root privilege to change any cpu affinity.
>>>>
>>>> Now, if we do the checking in rte_eal_cpu_init(), those lcores will be
>>>> flagged as undetected (in my older implementation) and leads to failure.
>>>> To make it correct, we would always add "taskset mask" (or other ways)
>>>> before DPDK application cmd lines.
>>>>
>>>> How do you think?
>>> I still think it sounds like something that should be done by default
>>> and maybe be overridable with some flag, rather than the other way
>>> around. Another alternative might be detecting the cores always but if
>>> running as root, override but with a warning.
>> For your second solution, only root can setaffinity to isolcpus?
>> Your first solution seems like a promising way for me.
>>
>>> But I dont know, just wondering. To look at it from another angle: why
>>> would somebody use this new --avail-cores option and in what
>>> situation, if things "just work" otherwise anyway?
>> For DPDK applications, the most common case to initialize DPDK is like
>> this: "$dpdk-app [options for DPDK] -- [options for app]", so users need
>> to specify which cores to run and how much hugepages are used. Suppose
>> we need this dpdk-app to run in a container, users already give those
>> information when they build up the cgroup for it to run inside, this
>> option or this patch is to make DPDK more smart to discover how much
>> resource will be used. Make sense?
> But then, all we need might be just a script that would extract this information from the system
> and form a proper cmdline parameter for DPDK?

Yes, a script will work. Or to construct (argc, argv) to call 
rte_eal_init() in the application. But as Neil Horman once suggested, a 
simple pthread_getaffinity_np() will get all things done. So if it worth 
a patch here?

Thanks,
Jianfeng

> Konstantin
>
>> Thanks,
>> Jianfeng
>>
>>
>>>      - Panu -
>>>