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

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-05-19 10:25, Tan, Jianfeng:
> On 5/18/2016 8:46 PM, David Marchand wrote:
> > On Wed, Mar 9, 2016 at 2:05 PM, Panu Matilainen <pmatilai@redhat.com> wrote:
> >> On 03/08/2016 07:38 PM, Tan, Jianfeng wrote:
> >>> 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@intel.com>
> >>>>> Acked-by: Neil Horman <nhorman@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.
> >>
> >> 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?
> > +1 and I don't even see why we should have an option to disable this,
> > since taskset would do the job.
> >
> > Looking at your special case, if the user did set an isolcpus option
> > for another use, with no -c/-l, I understand the dpdk application
> > won't care too much about it.
> > So, this seems like somehow rude to the rest of the system and unwanted.
> 
> The case you mentioned above is not the case I mean. But you make your 
> point about this one.
> The case I originally mean: user sets an isolcpus option for DPDK 
> applications. Originally, DPDK apps would be started without any 
> problem. But for now, fail to start them because the required cores are 
> excluded before -c/-l. As per your comments following, we can add a 
> warning message (or should we quit on this situation?). But it indeed 
> has an effect on old users (they should changed to use "taskset 
> ./dpdk_app ..."). Do you think it's a problem?

There is no activity on this patch.
Jianfeng, do not hesitate to ping if needed.
Should we class this patch as "changes requested"?