From: Sukadev Bhattiprolu <sukadev@linux•vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@au1•ibm.com>
Cc: Michael Neuling <mikey@neuling•org>,
Michael Ellerman <mpe@ellerman•id.au>,
stewart@linux•vnet.ibm.com, linuxppc-dev@ozlabs•org,
linux-kernel@vger•kernel.org, apopple@au1•ibm.com,
oohall@gmail•com
Subject: Re: [PATCH v6 14/17] powerpc: Add support for setting SPRN_TIDR
Date: Mon, 14 Aug 2017 12:27:15 -0700 [thread overview]
Message-ID: <20170814192715.GC24096@us.ibm.com> (raw)
In-Reply-To: <1502717435.4493.29.camel@au1.ibm.com>
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.
next prev parent reply other threads:[~2017-08-14 19:27 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-08 23:06 [PATCH v6 00/17] powerpc/vas: Enable VAS Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 01/17] powerpc/vas: Define macros, register fields and structures Sukadev Bhattiprolu
2017-08-14 5:21 ` Michael Ellerman
2017-08-14 6:05 ` Nicholas Piggin
2017-08-14 11:00 ` Michael Ellerman
2017-08-14 19:14 ` Sukadev Bhattiprolu
2017-08-16 12:07 ` Michael Ellerman
2017-08-16 23:07 ` Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 02/17] powerpc/vas: Move GET_FIELD/SET_FIELD to vas.h Sukadev Bhattiprolu
2017-08-14 7:26 ` Michael Ellerman
2017-08-08 23:06 ` [PATCH v6 03/17] powerpc/vas: Define vas_init() and vas_exit() Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 04/17] powerpc/vas: Define helpers to access MMIO regions Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 05/17] powerpc/vas: Define helpers to init window context Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 06/17] powerpc/vas: Define helpers to alloc/free windows Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 07/17] powerpc/vas: Define vas_win_paste_addr() Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 08/17] powerpc/vas: Define vas_win_id() Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 09/17] powerpc/vas: Define vas_rx_win_open() interface Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 10/17] " Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 11/17] powerpc/vas: Define vas_win_close() interface Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 12/17] powerpc/vas: Define vas_tx_win_open() Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 13/17] powerpc/vas: Define copy/paste interfaces Sukadev Bhattiprolu
2017-08-08 23:06 ` [PATCH v6 14/17] powerpc: Add support for setting SPRN_TIDR Sukadev Bhattiprolu
2017-08-14 7:02 ` Michael Neuling
2017-08-14 13:30 ` Benjamin Herrenschmidt
2017-08-14 19:27 ` Sukadev Bhattiprolu [this message]
2017-08-14 11:16 ` Michael Ellerman
2017-08-14 20:03 ` Sukadev Bhattiprolu
2017-08-14 22:25 ` Benjamin Herrenschmidt
2017-08-14 22:23 ` Benjamin Herrenschmidt
2017-08-08 23:07 ` [PATCH v6 15/17] powerpc/vas: Define window open ioctls API Sukadev Bhattiprolu
2017-08-08 23:07 ` [PATCH v6 16/17] powerpc/vas: Implement a simple FTW driver Sukadev Bhattiprolu
2017-08-14 6:53 ` Michael Ellerman
2017-08-08 23:07 ` [PATCH v6 17/17] powerpc/vas: Document FTW API/usage Sukadev Bhattiprolu
2017-08-14 10:43 ` Michael Neuling
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