xen/23562-xenpaging_remove_unused_spinlock_in_pager.patch

changeset:   23562:8a7f52c59d64
user:        Olaf Hering <olaf@aepfle.de>
date:        Fri Jun 10 10:47:02 2011 +0200
files:       tools/xenpaging/mem_event.h tools/xenpaging/spinlock.h tools/xenpaging/xenpaging.c tools/xenpaging/xenpaging.h
description:
xenpaging: remove unused spinlock in pager

The spinlock code in the pager is a no-op because xenpaging is a single
threaded application. There is no locking when put_response() places a
response into the ringbuffer.
The only locking is inside the hypervisor, where mem_event_put_request() and
mem_event_get_response() lock the ringbuffer to protect multiple vcpus from
each other.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Committed-by: Ian Jackson <ian.jackson.citrix.com>


---
 tools/xenpaging/mem_event.h |    5 ---
 tools/xenpaging/spinlock.h  |   69 --------------------------------------------
 tools/xenpaging/xenpaging.c |   12 -------
 tools/xenpaging/xenpaging.h |    1 
 4 files changed, 87 deletions(-)

Index: xen-4.1.2-testing/tools/xenpaging/mem_event.h
===================================================================
--- xen-4.1.2-testing.orig/tools/xenpaging/mem_event.h
+++ xen-4.1.2-testing/tools/xenpaging/mem_event.h
@@ -25,7 +25,6 @@
 #define __XEN_MEM_EVENT_H__
 
 
-#include "spinlock.h"
 #include "xc.h"
 #include <xc_private.h>
 
@@ -33,9 +32,6 @@
 #include <xen/mem_event.h>
 
 
-#define mem_event_ring_lock_init(_m)  spin_lock_init(&(_m)->ring_lock)
-#define mem_event_ring_lock(_m)       spin_lock(&(_m)->ring_lock)
-#define mem_event_ring_unlock(_m)     spin_unlock(&(_m)->ring_lock)
 
 
 typedef struct mem_event {
@@ -45,7 +41,6 @@ typedef struct mem_event {
     mem_event_back_ring_t back_ring;
     mem_event_shared_page_t *shared_page;
     void *ring_page;
-    spinlock_t ring_lock;
 } mem_event_t;
 
 
Index: xen-4.1.2-testing/tools/xenpaging/spinlock.h
===================================================================
--- xen-4.1.2-testing.orig/tools/xenpaging/spinlock.h
+++ /dev/null
@@ -1,69 +0,0 @@
-/******************************************************************************
- * tools/xenpaging/spinlock.h
- *
- * Spinlock implementation.
- *
- * Copyright (c) 2009 Citrix Systems, Inc. (Patrick Colp)
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
- */
-
-
-#ifndef __SPINLOCK_H__
-#define __SPINLOCK_H__
-
-
-#include "bitops.h"
-
-
-#define SPIN_LOCK_UNLOCKED 0
-
-
-typedef int spinlock_t;
-
-
-static inline void spin_lock(spinlock_t *lock)
-{
-    while ( test_and_set_bit(1, lock) );
-}
-
-static inline void spin_lock_init(spinlock_t *lock)
-{
-    *lock = SPIN_LOCK_UNLOCKED;
-}
-
-static inline void spin_unlock(spinlock_t *lock)
-{
-    *lock = SPIN_LOCK_UNLOCKED;
-}
-
-static inline int spin_trylock(spinlock_t *lock)
-{
-    return !test_and_set_bit(1, lock);
-}
-
-
-#endif // __SPINLOCK_H__
-
-
-/*
- * Local variables:
- * mode: C
- * c-set-style: "BSD"
- * c-basic-offset: 4
- * tab-width: 4
- * indent-tabs-mode: nil
- * End:
- */
Index: xen-4.1.2-testing/tools/xenpaging/xenpaging.c
===================================================================
--- xen-4.1.2-testing.orig/tools/xenpaging/xenpaging.c
+++ xen-4.1.2-testing/tools/xenpaging/xenpaging.c
@@ -32,7 +32,6 @@
 #include <xen/mem_event.h>
 
 #include "bitops.h"
-#include "spinlock.h"
 #include "file_ops.h"
 #include "xc.h"
 
@@ -127,9 +126,6 @@ static xenpaging_t *xenpaging_init(domid
     BACK_RING_INIT(&paging->mem_event.back_ring,
                    (mem_event_sring_t *)paging->mem_event.ring_page,
                    PAGE_SIZE);
-
-    /* Initialise lock */
-    mem_event_ring_lock_init(&paging->mem_event);
     
     /* Initialise Xen */
     rc = xc_mem_event_enable(xch, paging->mem_event.domain_id,
@@ -302,8 +298,6 @@ static int get_request(mem_event_t *mem_
     mem_event_back_ring_t *back_ring;
     RING_IDX req_cons;
 
-    mem_event_ring_lock(mem_event);
-
     back_ring = &mem_event->back_ring;
     req_cons = back_ring->req_cons;
 
@@ -315,8 +309,6 @@ static int get_request(mem_event_t *mem_
     back_ring->req_cons = req_cons;
     back_ring->sring->req_event = req_cons + 1;
 
-    mem_event_ring_unlock(mem_event);
-
     return 0;
 }
 
@@ -325,8 +317,6 @@ static int put_response(mem_event_t *mem
     mem_event_back_ring_t *back_ring;
     RING_IDX rsp_prod;
 
-    mem_event_ring_lock(mem_event);
-
     back_ring = &mem_event->back_ring;
     rsp_prod = back_ring->rsp_prod_pvt;
 
@@ -338,8 +328,6 @@ static int put_response(mem_event_t *mem
     back_ring->rsp_prod_pvt = rsp_prod;
     RING_PUSH_RESPONSES(back_ring);
 
-    mem_event_ring_unlock(mem_event);
-
     return 0;
 }
 
Index: xen-4.1.2-testing/tools/xenpaging/xenpaging.h
===================================================================
--- xen-4.1.2-testing.orig/tools/xenpaging/xenpaging.h
+++ xen-4.1.2-testing/tools/xenpaging/xenpaging.h
@@ -25,7 +25,6 @@
 #define __XEN_PAGING2_H__
 
 
-#include "spinlock.h"
 #include "xc.h"
 #include <xc_private.h>