Messages in this thread | | | Date | Mon, 14 Aug 2017 12:27:15 -0700 | From | Sukadev Bhattiprolu <> | Subject | Re: [PATCH v6 14/17] powerpc: Add support for setting SPRN_TIDR |
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Benjamin Herrenschmidt [benh@au1.ibm.com] wrote: > On Mon, 2017-08-14 at 17:02 +1000, Michael Neuling wrote: > > > +/* > > > + * We need to assign an unique thread id to each thread in a process. This > > > + * thread id is intended to be used with the Fast Thread-wakeup (aka Core- > > > + * to-core wakeup) mechanism being implemented on top of Virtual Accelerator > > > + * Switchboard (VAS). > > > + * > > > + * To get a unique thread-id per process we could simply use task_pid_nr() > > > + * but the problem is that task_pid_nr() is not yet available for the thread > > > + * when copy_thread() is called. Fixing that would require changing more > > > + * intrusive arch-neutral code in code path in copy_process()?. > > > + * > > > + * Further, to assign unique thread ids within each process, we need an > > > + * atomic field (or an IDR) in task_struct, which again intrudes into the > > > + * arch-neutral code. > > > > Really? > > > > > + * So try to assign globally unique thraed ids for now. > > > > Yuck!
I know :-) copy_process() has:
retval = copy_thread_tls(clone_flags, stack_start, stack_size, p, tls); if (retval) goto bad_fork_cleanup_io;
if (pid != &init_struct_pid) { pid = alloc_pid(p->nsproxy->pid_ns_for_children); if (IS_ERR(pid)) {
so copy_thread() is called before a pid_nr is assigned to the task.
But see also response to Michael Ellerman.
> > Also CAPI has size limits for the TIDR afaik
Ok.
> > Ben.
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