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

Ananyev, Konstantin konstantin.ananyev at intel.com
Wed Mar 9 15:01:18 CET 2016



> -----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? 
Konstantin

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



More information about the dev mailing list