Add PCU (Per-CPU Unit) - an interface to manage synchronization of any trunk
authorrmind <rmind@NetBSD.org>
Thu, 17 Feb 2011 18:32:29 +0000
branchtrunk
changeset 198003 83bcc682459a
parent 198002 079fe1ae00db
child 198004 8ae80f74bf70
Add PCU (Per-CPU Unit) - an interface to manage synchronization of any per CPU context tied with an LWP. Main use - lazy FPU handling on SMP. Requested by matt@, will be used on mips64. Note: implementation will be improved to use IPIs before adopting on x86. OK ad@.
sys/conf/files
sys/kern/subr_pcu.c
sys/sys/cpu_data.h
sys/sys/lwp.h
sys/sys/pcu.h
--- a/sys/conf/files	Thu Feb 17 18:26:20 2011 +0000
+++ b/sys/conf/files	Thu Feb 17 18:32:29 2011 +0000
@@ -1,4 +1,4 @@
-#	$NetBSD: files,v 1.998 2011/02/09 21:21:32 macallan Exp $
+#	$NetBSD: files,v 1.999 2011/02/17 18:32:29 rmind Exp $
 #	@(#)files.newconf	7.5 (Berkeley) 5/10/93
 
 version 	20100430
@@ -1533,6 +1533,7 @@
 file	kern/subr_lwp_specificdata.c
 file	kern/subr_once.c
 file	kern/subr_optstr.c
+file	kern/subr_pcu.c
 file	kern/subr_percpu.c
 file	kern/subr_pool.c
 file	kern/subr_prf.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sys/kern/subr_pcu.c	Thu Feb 17 18:32:29 2011 +0000
@@ -0,0 +1,258 @@
+/*	$NetBSD: subr_pcu.c,v 1.1 2011/02/17 18:32:29 rmind Exp $	*/
+
+/*-
+ * Copyright (c) 2011 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Mindaugas Rasiukevicius.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+ * Per CPU Unit (PCU) - is an interface to manage synchronization of any
+ * per CPU context (unit) tied with LWP context.  Typical use: FPU state.
+ *
+ * Concurrency notes:
+ *
+ *	PCU state may be loaded only by the current LWP, that is, curlwp.
+ *	Therefore, only LWP itself can set a CPU for lwp_t::l_pcu_cpu[id].
+ *
+ *	Request for a PCU release can be from owner LWP (whether PCU state
+ *	is on current CPU or remote CPU) or any other LWP running on that
+ *	CPU (in such case, owner LWP is on a remote CPU or sleeping).
+ *
+ *	In any case, PCU state can only be changed from the running CPU.
+ *	If said PCU state is on the remote CPU, a cross-call will be sent
+ *	by the owner LWP.  Therefore struct cpu_info::ci_pcu_curlwp[id]
+ *	may only be changed by current CPU, and lwp_t::l_pcu_cpu[id] may
+ *	only be unset by the CPU which has PCU state loaded.
+ *
+ *	There is a race condition: LWP may have a PCU state on a remote CPU,
+ *	which it requests to be released via cross-call.  At the same time,
+ *	other LWP on remote CPU might release existing PCU state and load
+ *	its own one.  Cross-call may arrive after this and release different
+ *	PCU state than intended.  In such case, such LWP would re-load its
+ *	PCU state again.
+ */
+
+#include <sys/cdefs.h>
+__KERNEL_RCSID(0, "$NetBSD: subr_pcu.c,v 1.1 2011/02/17 18:32:29 rmind Exp $");
+
+#include <sys/param.h>
+#include <sys/cpu.h>
+#include <sys/lwp.h>
+#include <sys/pcu.h>
+#include <sys/xcall.h>
+
+#define	PCU_SAVE		0x01	/* Save PCU state to the LWP. */
+#define	PCU_RELEASE		0x02	/* Release PCU state on the CPU. */
+
+#if 0
+/*
+ * pcu_init_lwp: initialize PCU structures for LWP.
+ */
+void
+pcu_init_lwp(lwp_t *l)
+{
+
+	memset(l->l_pcu_cpu, 0, sizeof(uint32_t) * PCU_UNIT_COUNT);
+	l->l_pcu_used = 0;
+}
+#endif
+
+/*
+ * pcu_cpu_op: save/release PCU state on the current CPU.
+ *
+ * => Must be called at IPL_SOFTCLOCK or from the soft-interrupt.
+ */
+static void
+pcu_cpu_op(const pcu_ops_t *pcu, const int flags)
+{
+	const u_int id = pcu->pcu_id;
+	struct cpu_info *ci = curcpu();
+	lwp_t *l = ci->ci_pcu_curlwp[id];
+
+	/* If no state - nothing to do. */
+	if (l == NULL) {
+		return;
+	}
+	if (flags & PCU_SAVE) {
+		pcu->pcu_state_save(l);
+	}
+	if (flags & PCU_RELEASE) {
+		ci->ci_pcu_curlwp[id] = NULL;
+		l->l_pcu_cpu[id] = NULL;
+	}
+}
+
+/*
+ * pcu_lwp_op: perform PCU state save, release or both operations on LWP.
+ */
+static void
+pcu_lwp_op(const pcu_ops_t *pcu, lwp_t *l, int flags)
+{
+	const u_int id = pcu->pcu_id;
+	struct cpu_info *ci;
+	uint64_t where;
+	int s;
+
+	/*
+	 * Caller should have re-checked if there is any state to manage.
+	 * Block the interrupts and inspect again, since cross-call sent
+	 * by remote CPU could have changed the state.
+	 */
+	s = splsoftclock();
+	ci = l->l_pcu_cpu[id];
+	if (ci == curcpu()) {
+		/*
+		 * State is on the current CPU - just perform the operations.
+		 */
+		KASSERT(ci->ci_pcu_curlwp[id] == l);
+
+		if (flags & PCU_SAVE) {
+			pcu->pcu_state_save(l);
+		}
+		if (flags & PCU_RELEASE) {
+			ci->ci_pcu_curlwp[id] = NULL;
+			l->l_pcu_cpu[id] = NULL;
+		}
+		splx(s);
+		return;
+	}
+	splx(s);
+
+	if (__predict_false(ci == NULL)) {
+		/* Cross-call has won the race - no state to manage. */
+		return;
+	}
+
+	/*
+	 * State is on the remote CPU - perform the operations there.
+	 * Note: there is a race condition; see description in the top.
+	 */
+	where = xc_unicast(XC_HIGHPRI, (xcfunc_t)pcu_cpu_op,
+	    __UNCONST(pcu), (void *)(uintptr_t)flags, ci);
+	xc_wait(where);
+
+	KASSERT((flags & PCU_RELEASE) == 0 || l->l_pcu_cpu[id] == NULL);
+}
+
+/*
+ * pcu_load: load/initialize the PCU state of current LWP on current CPU.
+ */
+void
+pcu_load(const pcu_ops_t *pcu)
+{
+	const u_int id = pcu->pcu_id;
+	struct cpu_info *ci, *curci;
+	lwp_t *l = curlwp;
+	uint64_t where;
+	int s;
+
+	KASSERT(!cpu_intr_p() && !cpu_softintr_p());
+
+	s = splsoftclock();
+	curci = curcpu();
+	ci = l->l_pcu_cpu[id];
+
+	/* Does this CPU already have our PCU state loaded? */
+	if (ci == curci) {
+		KASSERT(curci->ci_pcu_curlwp[id] == l);
+		splx(s);
+		return;
+	}
+
+	/* If PCU state of this LWP is on the remote CPU - save it there. */
+	if (ci) {
+		splx(s);
+		/* Note: there is a race; see description in the top. */
+		where = xc_unicast(XC_HIGHPRI, (xcfunc_t)pcu_cpu_op,
+		    __UNCONST(pcu), (void *)(PCU_SAVE | PCU_RELEASE), ci);
+		xc_wait(where);
+
+		/* Enter IPL_SOFTCLOCK and re-fetch the current CPU. */
+		s = splsoftclock();
+		curci = curcpu();
+	}
+	KASSERT(l->l_pcu_cpu[id] == NULL);
+
+	/* Save the PCU state on the current CPU, if there is any. */
+	pcu_cpu_op(pcu, PCU_SAVE | PCU_RELEASE);
+	KASSERT(curci->ci_pcu_curlwp[id] == NULL);
+
+	/*
+	 * Finally, load the state for this LWP on this CPU.  Indicate to
+	 * load function whether PCU was used before.  Note the usage.
+	 */
+	pcu->pcu_state_load(l, ((1 << id) & l->l_pcu_used) != 0);
+	curci->ci_pcu_curlwp[id] = l;
+	l->l_pcu_cpu[id] = curci;
+	l->l_pcu_used |= (1 << id);
+	splx(s);
+}
+
+/*
+ * pcu_discard: discard the PCU state of current LWP.
+ */
+void
+pcu_discard(const pcu_ops_t *pcu)
+{
+	const u_int id = pcu->pcu_id;
+	lwp_t *l = curlwp;
+
+	KASSERT(!cpu_intr_p() && !cpu_softintr_p());
+
+	if (__predict_true(l->l_pcu_cpu[id] == NULL)) {
+		return;
+	}
+	pcu_lwp_op(pcu, l, PCU_RELEASE);
+	l->l_pcu_used &= ~(1 << id);
+}
+
+/*
+ * pcu_save_lwp: save PCU state to the given LWP.
+ */
+void
+pcu_save_lwp(const pcu_ops_t *pcu, lwp_t *l)
+{
+	const u_int id = pcu->pcu_id;
+
+	KASSERT(!cpu_intr_p() && !cpu_softintr_p());
+
+	if (__predict_true(l->l_pcu_cpu[id] == NULL)) {
+		return;
+	}
+	pcu_lwp_op(pcu, l, PCU_SAVE | PCU_RELEASE);
+}
+
+/*
+ * pcu_used: return true if PCU was used (pcu_load() case) by the LWP.
+ */
+bool
+pcu_used(const pcu_ops_t *pcu, lwp_t *l)
+{
+	const u_int id = pcu->pcu_id;
+
+	return l->l_pcu_used & (1 << id);
+}
--- a/sys/sys/cpu_data.h	Thu Feb 17 18:26:20 2011 +0000
+++ b/sys/sys/cpu_data.h	Thu Feb 17 18:32:29 2011 +0000
@@ -1,4 +1,4 @@
-/*	$NetBSD: cpu_data.h,v 1.32 2010/12/20 00:25:47 matt Exp $	*/
+/*	$NetBSD: cpu_data.h,v 1.33 2011/02/17 18:32:29 rmind Exp $	*/
 
 /*-
  * Copyright (c) 2004, 2006, 2007, 2008 The NetBSD Foundation, Inc.
@@ -39,6 +39,7 @@
 
 #include <sys/sched.h>	/* for schedstate_percpu */
 #include <sys/condvar.h>
+#include <sys/pcu.h>
 #include <sys/percpu_types.h>
 #include <sys/queue.h>
 
@@ -75,6 +76,8 @@
 	cpuid_t		cpu_core_id;
 	cpuid_t		cpu_smt_id;
 
+	struct lwp * volatile cpu_pcu_curlwp[PCU_UNIT_COUNT];
+
 	/*
 	 * This section is mostly CPU-private.
 	 */
@@ -116,6 +119,7 @@
 #define	ci_lockstat		ci_data.cpu_lockstat
 #define	ci_spin_locks2		ci_data.cpu_spin_locks2
 #define	ci_lkdebug_recurse	ci_data.cpu_lkdebug_recurse
+#define	ci_pcu_curlwp		ci_data.cpu_pcu_curlwp
 
 #define	ci_package_id		ci_data.cpu_package_id
 #define	ci_core_id		ci_data.cpu_core_id
--- a/sys/sys/lwp.h	Thu Feb 17 18:26:20 2011 +0000
+++ b/sys/sys/lwp.h	Thu Feb 17 18:32:29 2011 +0000
@@ -1,4 +1,4 @@
-/*	$NetBSD: lwp.h,v 1.142 2011/01/28 16:58:27 pooka Exp $	*/
+/*	$NetBSD: lwp.h,v 1.143 2011/02/17 18:32:29 rmind Exp $	*/
 
 /*-
  * Copyright (c) 2001, 2006, 2007, 2008, 2009, 2010
@@ -39,6 +39,7 @@
 #include <sys/callout.h>
 #include <sys/mutex.h>
 #include <sys/condvar.h>
+#include <sys/pcu.h>
 #include <sys/signalvar.h>
 #include <sys/sched.h>
 #include <sys/specificdata.h>
@@ -123,6 +124,9 @@
 	callout_t	l_timeout_ch;	/* !: callout for tsleep */
 	u_int		l_emap_gen;	/* !: emap generation number */
 
+	struct cpu_info	* volatile l_pcu_cpu[PCU_UNIT_COUNT];
+	uint32_t	l_pcu_used;
+
 	/* Process level and global state, misc. */
 	LIST_ENTRY(lwp)	l_list;		/* a: entry on list of all LWPs */
 	void		*l_ctxlink;	/* p: uc_link {get,set}context */
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sys/sys/pcu.h	Thu Feb 17 18:32:29 2011 +0000
@@ -0,0 +1,57 @@
+/*	$NetBSD: pcu.h,v 1.1 2011/02/17 18:32:29 rmind Exp $	*/
+
+/*-
+ * Copyright (c) 2011 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Mindaugas Rasiukevicius.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_PCU_H_
+#define _SYS_PCU_H_
+
+#if !defined(_KERNEL) && !defined(_KMEMUSER)
+#error "Kernel-only header"
+#endif
+
+/*
+ * Default: one PCU for MD.
+ */
+#ifndef	PCU_UNIT_COUNT
+#define	PCU_UNIT_COUNT		1
+#endif
+
+typedef struct {
+	u_int	pcu_id;
+	void	(*pcu_state_save)(lwp_t *);
+	void	(*pcu_state_load)(lwp_t *, bool);
+} pcu_ops_t;
+
+void	pcu_load(const pcu_ops_t *);
+void	pcu_save_lwp(const pcu_ops_t *, lwp_t *);
+void	pcu_discard(const pcu_ops_t *);
+bool	pcu_used(const pcu_ops_t *, lwp_t *);
+
+#endif