Re: [Starpu-devel] A possible bug in StarPU 1.3.xx

[Mirko Myllykoski <mirkom@cs.umu.se>]

Hi,

Should I consider parallel task policies to be a deprecated feature of 
StarPU? If so, what is the recommended way to implement parallel tasks? 
I read about "clustering" but the documentation of that feature appears 
to be very limited.

 - Mirko

On 2018-09-28 09:29, Olivier Aumage wrote:
> Hi Mirko,
>
> The issue is actually the "pheft" policy selected for the sched
> context being created. The "pheft" policy has always been experimental
> and has not received much work for quite a long time.
>
> The "peager" policy is also experimental but in a reasonably stable
> state. When replacing the "pheft" policy by "peager"  (or one of the
> sequential task policies) the program completes for me.
>
> Best regards,
> --
> Olivier Aumage
>
> > Le 27 sept. 2018 à 14:45, Mirko Myllykoski <mirkom@cs.umu.se> a écrit 
> > :
> >
> > Hi,
> >
> > I believe that I have found a bug from StarPU 1.3.xx. I am
> > trying to create a scheduling context that contains a set of
> > CPU and CUDA workers. The code functions perfectly with
> > StarPU 1.2.6 but leads to a segmentation fault with StarPU
> > 1.3.xx. I have isolated the problem to the following code
> > lines:
> >
> > ========== CODE BEGINS ==========
> >
> > #include <starpu.h>
> >
> > int main()
> > {
> >    if (starpu_init(NULL) != 0)
> >        abort();
> >
> >    // get CPU workers
> >    int cpu_worker_ids[STARPU_NMAXWORKERS];
> >    int cpu_worker_count = starpu_worker_get_ids_by_type(
> >        STARPU_CPU_WORKER, cpu_worker_ids, STARPU_NMAXWORKERS);
> >
> >    // get CUDA workers
> >    int gpu_worker_ids[STARPU_NMAXWORKERS];
> >    int gpu_worker_count = starpu_worker_get_ids_by_type(
> >        STARPU_CUDA_WORKER, gpu_worker_ids, STARPU_NMAXWORKERS);
> >
> >    // create a parallel scheduling context and add all CPU
> >    // workers to it
> >    unsigned parallel_ctx = starpu_sched_ctx_create(
> >        cpu_worker_ids, cpu_worker_count, "parallel_cxt",
> >        STARPU_SCHED_CTX_POLICY_NAME, "pheft", 0);
> >
> >    // add CUDA workers, if any, to the parallel scheduling
> >    // context
> >    if (0 < gpu_worker_count)
> >        starpu_sched_ctx_add_workers(   // <=== *** LINE 21 ***
> >            gpu_worker_ids, gpu_worker_count, parallel_ctx);
> >
> >    starpu_sched_ctx_delete(parallel_ctx);
> >    starpu_shutdown();
> > }
> >
> > ==========  CODE ENDS  ==========
> >
> > GDB backtrace:
> >
> > ========== GDB BEGINS  ==========
> >
> > (gdb) bt
> > #0  0x00007ffff7846d29 in lws_select_victim (ws=0x555555a14250, 
> > sched_ctx_id=0, workerid=3) at 
> > sched_policies/work_stealing_policy.c:773
> > #1  0x00007ffff7845ff8 in ws_pop_task (sched_ctx_id=0) at 
> > sched_policies/work_stealing_policy.c:567
> > #2  0x00007ffff782a2f0 in _starpu_pop_task (worker=0x7ffff7ba31c8 
> > <_starpu_config+5640>) at core/sched_policy.c:871
> > #3  0x00007ffff78629aa in _starpu_get_worker_task 
> > (worker=0x7ffff7ba31c8 <_starpu_config+5640>, workerid=3, memnode=0) 
> > at drivers/driver_common/driver_common.c:377
> > #4  0x00007ffff7915750 in _starpu_cpu_driver_run_once 
> > (cpu_worker=0x7ffff7ba31c8 <_starpu_config+5640>) at 
> > drivers/cpu/driver_cpu.c:303
> > #5  0x00007ffff7915dd8 in _starpu_cpu_worker (arg=0x7ffff7ba31c8 
> > <_starpu_config+5640>) at drivers/cpu/driver_cpu.c:407
> > #6  0x00007ffff6f756db in start_thread (arg=0x7fffbbfff700) at 
> > pthread_create.c:463
> > #7  0x00007ffff74b288f in clone () at 
> > ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
> >
> > ==========  GDB ENDS   ==========
> >
> > Or, if I set STARPU_SCHED=prio, I get:
> >
> > ========== GDB BEGINS  ==========
> >
> > (gdb) bt
> > #0  0x00007ffff783c59e in _starpu_sched_ctx_list_remove_elt 
> > (list=0x7ffff7ba25f8 <_starpu_config+2616>, rm=0x5555558979c0) at 
> > core/sched_ctx_list.c:262
> > #1  0x00007ffff783c6ad in _starpu_sched_ctx_list_move 
> > (list=0x7ffff7ba25f8 <_starpu_config+2616>, sched_ctx=1, prio_to=1) at 
> > core/sched_ctx_list.c:293
> > #2  0x00007ffff78390d3 in set_priority_on_notified_workers 
> > (workers=0x7fffffffd9b0, nworkers=1, sched_ctx_id=1, priority=1) at 
> > core/sched_ctx.c:2099
> > #3  0x00007ffff78356d9 in add_notified_workers 
> > (workerids=0x7fffffffd9b0, nworkers=1, sched_ctx_id=1) at 
> > core/sched_ctx.c:1228
> > #4  0x00007ffff7835fe7 in starpu_sched_ctx_add_workers 
> > (workers_to_add=0x7fffffffd9b0, nworkers_to_add=1, sched_ctx_id=1) at 
> > core/sched_ctx.c:1316
> > #5  0x0000555555554a54 in main () at main.c:21
> >
> > ==========  GDB ENDS   ==========
> >
> > Best Regards,
> > Mirko Myllykoski
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