From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xWQc538DVzDqZ8 for ; Tue, 15 Aug 2017 05:27:33 +1000 (AEST) Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) by bilbo.ozlabs.org (Postfix) with ESMTP id 3xWQc51y1yz8vNK for ; Tue, 15 Aug 2017 05:27:33 +1000 (AEST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3xWQc45Sbgz9t39 for ; Tue, 15 Aug 2017 05:27:32 +1000 (AEST) Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v7EJNn3j023977 for ; Mon, 14 Aug 2017 15:27:30 -0400 Received: from e16.ny.us.ibm.com (e16.ny.us.ibm.com [129.33.205.206]) by mx0b-001b2d01.pphosted.com with ESMTP id 2cbe3j3c47-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 14 Aug 2017 15:27:29 -0400 Received: from localhost by e16.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 14 Aug 2017 15:27:29 -0400 Date: Mon, 14 Aug 2017 12:27:15 -0700 From: Sukadev Bhattiprolu To: Benjamin Herrenschmidt Cc: Michael Neuling , Michael Ellerman , 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 References: <1502233622-9330-1-git-send-email-sukadev@linux.vnet.ibm.com> <1502233622-9330-15-git-send-email-sukadev@linux.vnet.ibm.com> <1502694131.9844.7.camel@neuling.org> <1502717435.4493.29.camel@au1.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1502717435.4493.29.camel@au1.ibm.com> Message-Id: <20170814192715.GC24096@us.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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.