Re: [dpdk-dev] [RFC PATCH 0/7] support multi-phtread per lcore

["Walukiewicz, Miroslaw" <Miroslaw.Walukiewicz@intel.com>]

I have another question regarding your patch.

 Could we extend values returned by rte_lcore_id() to set them per thread (really the DPDK lcore is a pthread but started on specific core) instead of creating linear thread id. 

The patch would be much simpler and will work same way. The only change would be extending rte_lcore_id when rte_pthread_create() is called. 

The value __lcore_id has really an attribute __thread that means it is valid not only per CPU core but also per thread.

The mempools, timers, statistics would work without any modifications in that environment.

 I do not see any reason why old legacy DPDK applications would not work in that model. 

Mirek

> -----Original Message-----
> From: Liang, Cunming
> Sent: Monday, December 15, 2014 12:53 PM
> To: Walukiewicz, Miroslaw; dev@dpdk.org
> Subject: RE: [dpdk-dev] [RFC PATCH 0/7] support multi-phtread per lcore
> 
> Hi Mirek,
> 
> That sounds great.
> Looking forward to it.
> 
> -Cunming
> 
> > -----Original Message-----
> > From: Walukiewicz, Miroslaw
> > Sent: Monday, December 15, 2014 7:11 PM
> > To: Liang, Cunming; dev@dpdk.org
> > Subject: RE: [dpdk-dev] [RFC PATCH 0/7] support multi-phtread per lcore
> >
> > Hi Cunming,
> >
> > The timers could be used by any application/library started as a standard
> > pthread.
> > Each pthread needs to have assigned some identifier same way as you are
> doing
> > it for mempools (the rte_linear_thread_id and rte_lcore_id are good
> examples)
> >
> > I made series of patches extending the rte timers API to use with such kind
> of
> > identifier keeping existing API working also.
> >
> > I will send it soon.
> >
> > Mirek
> >
> >
> > > -----Original Message-----
> > > From: Liang, Cunming
> > > Sent: Friday, December 12, 2014 6:45 AM
> > > To: Walukiewicz, Miroslaw; dev@dpdk.org
> > > Subject: RE: [dpdk-dev] [RFC PATCH 0/7] support multi-phtread per lcore
> > >
> > > Thanks Mirek. That's a good point which wasn't mentioned in cover
> letter.
> > > For 'rte_timer', I only expect it be used within the 'legacy per-lcore'
> pthread.
> > > I'm appreciate if you can give me some cases which can't use it to fit.
> > > In case have to use 'rte_timer' in multi-pthread, there are some
> > > prerequisites and limitations.
> > > 1. Make sure thread local variable 'lcore_id' is set correctly (e.g. do
> pthread
> > > init by rte_pthread_prepare)
> > > 2. As 'rte_timer' is not preemptable, when using
> rte_timer_manager/reset in
> > > multi-pthread, make sure they're not on the same core.
> > >
> > > -Cunming
> > >
> > > > -----Original Message-----
> > > > From: Walukiewicz, Miroslaw
> > > > Sent: Thursday, December 11, 2014 5:57 PM
> > > > To: Liang, Cunming; dev@dpdk.org
> > > > Subject: RE: [dpdk-dev] [RFC PATCH 0/7] support multi-phtread per
> lcore
> > > >
> > > > Thank you Cunming for explanation.
> > > >
> > > > What about DPDK timers? They also depend on rte_lcore_id() to avoid
> > > spinlocks.
> > > >
> > > > Mirek
> > > >
> > > > > -----Original Message-----
> > > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Cunming
> Liang
> > > > > Sent: Thursday, December 11, 2014 3:05 AM
> > > > > To: dev@dpdk.org
> > > > > Subject: [dpdk-dev] [RFC PATCH 0/7] support multi-phtread per lcore
> > > > >
> > > > >
> > > > > Scope & Usage Scenario
> > > > > ========================
> > > > >
> > > > > DPDK usually pin pthread per core to avoid task switch overhead. It
> gains
> > > > > performance a lot, but it's not efficient in all cases. In some cases, it
> may
> > > > > too expensive to use the whole core for a lightweight workload. It's a
> > > > > reasonable demand to have multiple threads per core and each
> threads
> > > > > share CPU
> > > > > in an assigned weight.
> > > > >
> > > > > In fact, nothing avoid user to create normal pthread and using cgroup
> to
> > > > > control the CPU share. One of the purpose for the patchset is to clean
> the
> > > > > gaps of using more DPDK libraries in the normal pthread. In addition, it
> > > > > demonstrates performance gain by proactive 'yield' when doing idle
> loop
> > > > > in packet IO. It also provides several 'rte_pthread_*' APIs to easy life.
> > > > >
> > > > >
> > > > > Changes to DPDK libraries
> > > > > ==========================
> > > > >
> > > > > Some of DPDK libraries must run in DPDK environment.
> > > > >
> > > > > # rte_mempool
> > > > >
> > > > > In rte_mempool doc, it mentions a thread not created by EAL must
> not
> > > use
> > > > > mempools. The root cause is it uses a per-lcore cache inside
> mempool.
> > > > > And 'rte_lcore_id()' will not return a correct value.
> > > > >
> > > > > The patchset changes this a little. The index of mempool cache won't
> be a
> > > > > lcore_id. Instead of it, using a linear number generated by the
> allocator.
> > > > > For those legacy EAL per-lcore thread, it apply for an unique linear id
> > > > > during creation. For those normal pthread expecting to use
> > > rte_mempool, it
> > > > > requires to apply for a linear id explicitly. Now the mempool cache
> looks
> > > like
> > > > > a per-thread base. The linear ID actually identify for the linear thread
> id.
> > > > >
> > > > > However, there's another problem. The rte_mempool is not
> > > preemptable.
> > > > > The
> > > > > problem comes from rte_ring, so talk together in next section.
> > > > >
> > > > > # rte_ring
> > > > >
> > > > > rte_ring supports multi-producer enqueue and multi-consumer
> > > dequeue.
> > > > > But it's
> > > > > not preemptable. There's conversation talking about this before.
> > > > > http://dpdk.org/ml/archives/dev/2013-November/000714.html
> > > > >
> > > > > Let's say there's two pthreads running on the same core doing
> enqueue
> > > on
> > > > > the
> > > > > same rte_ring. If the 1st pthread is preempted by the 2nd pthread
> while
> > > it
> > > > > has
> > > > > already modified the prod.head, the 2nd pthread will spin until the 1st
> > > one
> > > > > scheduled agian. It causes time wasting. In addition, if the 2nd
> pthread
> > > has
> > > > > absolutely higer priority, it's more terrible.
> > > > >
> > > > > But it doesn't means we can't use. Just need to narrow down the
> > > situation
> > > > > when
> > > > > it's used by multi-pthread on the same core.
> > > > > - It CAN be used for any single-producer or single-consumer situation.
> > > > > - It MAY be used by multi-producer/consumer pthread whose
> scheduling
> > > > > policy
> > > > > are all SCHED_OTHER(cfs). User SHOULD aware of the performance
> > > penalty
> > > > > befor
> > > > > using it.
> > > > > - It MUST not be used by multi-producer/consumer pthread, while
> some
> > > of
> > > > > their
> > > > > scheduling policies is SCHED_FIFO or SCHED_RR.
> > > > >
> > > > >
> > > > > Performance
> > > > > ==============
> > > > >
> > > > > It loses performance by introducing task switching. On packet IO
> > > perspective,
> > > > > we can gain some back by improving IO effective rate. When the
> pthread
> > > do
> > > > > idle
> > > > > loop on an empty rx queue, it should proactively yield. We can also
> slow
> > > > > down
> > > > > rx for a bit while to take more advantage of the bulk receiving in the
> next
> > > > > loop. In practice, increase the rx ring size also helps to improve the
> > > overrall
> > > > > throughput.
> > > > >
> > > > >
> > > > > Cgroup Control
> > > > > ================
> > > > >
> > > > > Here's a simple example, there's four pthread doing packet IO on the
> > > same
> > > > > core.
> > > > > We expect the CPU share rate is 1:1:2:4.
> > > > > > mkdir /sys/fs/cgroup/cpu/dpdk
> > > > > > mkdir /sys/fs/cgroup/cpu/dpdk/thread0
> > > > > > mkdir /sys/fs/cgroup/cpu/dpdk/thread1
> > > > > > mkdir /sys/fs/cgroup/cpu/dpdk/thread2
> > > > > > mkdir /sys/fs/cgroup/cpu/dpdk/thread3
> > > > > > cd /sys/fs/cgroup/cpu/dpdk
> > > > > > echo 256 > thread0/cpu.shares
> > > > > > echo 256 > thread1/cpu.shares
> > > > > > echo 512 > thread2/cpu.shares
> > > > > > echo 1024 > thread3/cpu.shares
> > > > >
> > > > >
> > > > > -END-
> > > > >
> > > > > Any comments are welcome.
> > > > >
> > > > > Thanks
> > > > >
> > > > > *** BLURB HERE ***
> > > > >
> > > > > Cunming Liang (7):
> > > > >   eal: add linear thread id as pthread-local variable
> > > > >   mempool: use linear-tid as mempool cache index
> > > > >   ring: use linear-tid as ring debug stats index
> > > > >   eal: add simple API for multi-pthread
> > > > >   testpmd: support multi-pthread mode
> > > > >   sample: add new sample for multi-pthread
> > > > >   eal: macro for cpuset w/ or w/o CPU_ALLOC
> > > > >
> > > > >  app/test-pmd/cmdline.c                    |  41 +++++
> > > > >  app/test-pmd/testpmd.c                    |  84 ++++++++-
> > > > >  app/test-pmd/testpmd.h                    |   1 +
> > > > >  config/common_linuxapp                    |   1 +
> > > > >  examples/multi-pthread/Makefile           |  57 ++++++
> > > > >  examples/multi-pthread/main.c             | 232
> > > > ++++++++++++++++++++++++
> > > > >  examples/multi-pthread/main.h             |  46 +++++
> > > > >  lib/librte_eal/common/include/rte_eal.h   |  15 ++
> > > > >  lib/librte_eal/common/include/rte_lcore.h |  12 ++
> > > > >  lib/librte_eal/linuxapp/eal/eal_thread.c  | 282
> > > > > +++++++++++++++++++++++++++---
> > > > >  lib/librte_mempool/rte_mempool.h          |  22 +--
> > > > >  lib/librte_ring/rte_ring.h                |   6 +-
> > > > >  12 files changed, 755 insertions(+), 44 deletions(-)
> > > > >  create mode 100644 examples/multi-pthread/Makefile
> > > > >  create mode 100644 examples/multi-pthread/main.c
> > > > >  create mode 100644 examples/multi-pthread/main.h
> > > > >
> > > > > --
> > > > > 1.8.1.4