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

[Olivier Aumage <olivier.aumage@inria.fr>]

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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