[Xen-devel,30/57] ARM: new VGIC: Add IRQ sorting

Message ID 20180305160415.16760-31-andre.przywara@linaro.org
State New
Headers show
Series
  • New VGIC(-v2) implementation
Related show

Commit Message

Andre Przywara March 5, 2018, 4:03 p.m.
Adds the sorting function to cover the case where you have more IRQs
to consider than you have LRs. We consider their priorities.
This pulls in Linux' list_sort.c, which is a merge sort implementation
for linked lists. Apart from adding a full featured license header and
adjusting the #include file, nothing has been changed in this code.

This is based on Linux commit 8e4447457965, written by Christoffer Dall.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
---
Changelog RFC ... v1:
- use Linux coding style for list_sort.c

 xen/arch/arm/vgic/vgic.c    |  59 +++++++++++++++++
 xen/common/list_sort.c      | 157 ++++++++++++++++++++++++++++++++++++++++++++
 xen/include/xen/list_sort.h |  11 ++++
 3 files changed, 227 insertions(+)
 create mode 100644 xen/common/list_sort.c
 create mode 100644 xen/include/xen/list_sort.h

Comments

Julien Grall March 7, 2018, 11:06 a.m. | #1
Hi Andre,

On 03/05/2018 04:03 PM, Andre Przywara wrote:
> Adds the sorting function to cover the case where you have more IRQs
> to consider than you have LRs. We consider their priorities.
> This pulls in Linux' list_sort.c, which is a merge sort implementation
> for linked lists. Apart from adding a full featured license header and
> adjusting the #include file, nothing has been changed in this code.
> 
> This is based on Linux commit 8e4447457965, written by Christoffer Dall.
> 
> Signed-off-by: Andre Przywara <andre.przywara@linaro.org>

Again, you need to CC "THE REST" maintainers for this code. It would 
also make sense to have a separate patch for adding list_sort.c.

Cheers,

Patch

diff --git a/xen/arch/arm/vgic/vgic.c b/xen/arch/arm/vgic/vgic.c
index ae922815bd..efa6c67cb7 100644
--- a/xen/arch/arm/vgic/vgic.c
+++ b/xen/arch/arm/vgic/vgic.c
@@ -17,6 +17,7 @@ 
 
 #include <asm/bug.h>
 #include <asm/new_vgic.h>
+#include <xen/list_sort.h>
 #include <xen/sched.h>
 
 #include "vgic.h"
@@ -182,6 +183,64 @@  static struct vcpu *vgic_target_oracle(struct vgic_irq *irq)
     return NULL;
 }
 
+/*
+ * The order of items in the ap_lists defines how we'll pack things in LRs as
+ * well, the first items in the list being the first things populated in the
+ * LRs.
+ *
+ * A hard rule is that active interrupts can never be pushed out of the LRs
+ * (and therefore take priority) since we cannot reliably trap on deactivation
+ * of IRQs and therefore they have to be present in the LRs.
+ *
+ * Otherwise things should be sorted by the priority field and the GIC
+ * hardware support will take care of preemption of priority groups etc.
+ *
+ * Return negative if "a" sorts before "b", 0 to preserve order, and positive
+ * to sort "b" before "a".
+ */
+static int vgic_irq_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+    struct vgic_irq *irqa = container_of(a, struct vgic_irq, ap_list);
+    struct vgic_irq *irqb = container_of(b, struct vgic_irq, ap_list);
+    bool penda, pendb;
+    int ret;
+
+    spin_lock(&irqa->irq_lock);
+    spin_lock(&irqb->irq_lock);
+
+    if ( irqa->active || irqb->active )
+    {
+        ret = (int)irqb->active - (int)irqa->active;
+        goto out;
+    }
+
+    penda = irqa->enabled && irq_is_pending(irqa);
+    pendb = irqb->enabled && irq_is_pending(irqb);
+
+    if ( !penda || !pendb )
+    {
+        ret = (int)pendb - (int)penda;
+        goto out;
+    }
+
+    /* Both pending and enabled, sort by priority */
+    ret = irqa->priority - irqb->priority;
+out:
+    spin_unlock(&irqb->irq_lock);
+    spin_unlock(&irqa->irq_lock);
+    return ret;
+}
+
+/* Must be called with the ap_list_lock held */
+static void vgic_sort_ap_list(struct vcpu *vcpu)
+{
+    struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic;
+
+    ASSERT(spin_is_locked(&vgic_cpu->ap_list_lock));
+
+    list_sort(NULL, &vgic_cpu->ap_list_head, vgic_irq_cmp);
+}
+
 /*
  * Only valid injection if changing level for level-triggered IRQs or for a
  * rising edge.
diff --git a/xen/common/list_sort.c b/xen/common/list_sort.c
new file mode 100644
index 0000000000..af2b2f6519
--- /dev/null
+++ b/xen/common/list_sort.c
@@ -0,0 +1,157 @@ 
+/*
+ * list_sort.c: merge sort implementation for linked lists
+ * Copied from the Linux kernel (lib/list_sort.c)
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <xen/lib.h>
+#include <xen/list.h>
+
+#define MAX_LIST_LENGTH_BITS 20
+
+/*
+ * Returns a list organized in an intermediate format suited
+ * to chaining of merge() calls: null-terminated, no reserved or
+ * sentinel head node, "prev" links not maintained.
+ */
+static struct list_head *merge(void *priv,
+				int (*cmp)(void *priv, struct list_head *a,
+					struct list_head *b),
+				struct list_head *a, struct list_head *b)
+{
+	struct list_head head, *tail = &head;
+
+	while (a && b) {
+		/* if equal, take 'a' -- important for sort stability */
+		if ((*cmp)(priv, a, b) <= 0) {
+			tail->next = a;
+			a = a->next;
+		} else {
+			tail->next = b;
+			b = b->next;
+		}
+		tail = tail->next;
+	}
+	tail->next = a?:b;
+	return head.next;
+}
+
+/*
+ * Combine final list merge with restoration of standard doubly-linked
+ * list structure.  This approach duplicates code from merge(), but
+ * runs faster than the tidier alternatives of either a separate final
+ * prev-link restoration pass, or maintaining the prev links
+ * throughout.
+ */
+static void merge_and_restore_back_links(void *priv,
+				int (*cmp)(void *priv, struct list_head *a,
+					struct list_head *b),
+				struct list_head *head,
+				struct list_head *a, struct list_head *b)
+{
+	struct list_head *tail = head;
+	u8 count = 0;
+
+	while (a && b) {
+		/* if equal, take 'a' -- important for sort stability */
+		if ((*cmp)(priv, a, b) <= 0) {
+			tail->next = a;
+			a->prev = tail;
+			a = a->next;
+		} else {
+			tail->next = b;
+			b->prev = tail;
+			b = b->next;
+		}
+		tail = tail->next;
+	}
+	tail->next = a ? : b;
+
+	do {
+		/*
+		 * In worst cases this loop may run many iterations.
+		 * Continue callbacks to the client even though no
+		 * element comparison is needed, so the client's cmp()
+		 * routine can invoke cond_resched() periodically.
+		 */
+		if (unlikely(!(++count)))
+			(*cmp)(priv, tail->next, tail->next);
+
+		tail->next->prev = tail;
+		tail = tail->next;
+	} while (tail->next);
+
+	tail->next = head;
+	head->prev = tail;
+}
+
+/**
+ * list_sort - sort a list
+ * @priv: private data, opaque to list_sort(), passed to @cmp
+ * @head: the list to sort
+ * @cmp: the elements comparison function
+ *
+ * This function implements "merge sort", which has O(nlog(n))
+ * complexity.
+ *
+ * The comparison function @cmp must return a negative value if @a
+ * should sort before @b, and a positive value if @a should sort after
+ * @b. If @a and @b are equivalent, and their original relative
+ * ordering is to be preserved, @cmp must return 0.
+ */
+void list_sort(void *priv, struct list_head *head,
+		int (*cmp)(void *priv, struct list_head *a,
+			struct list_head *b))
+{
+	struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
+						-- last slot is a sentinel */
+	int lev;  /* index into part[] */
+	int max_lev = 0;
+	struct list_head *list;
+
+	if (list_empty(head))
+		return;
+
+	memset(part, 0, sizeof(part));
+
+	head->prev->next = NULL;
+	list = head->next;
+
+	while (list) {
+		struct list_head *cur = list;
+		list = list->next;
+		cur->next = NULL;
+
+		for (lev = 0; part[lev]; lev++) {
+			cur = merge(priv, cmp, part[lev], cur);
+			part[lev] = NULL;
+		}
+		if (lev > max_lev) {
+			if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
+				dprintk(XENLOG_DEBUG,
+					"list too long for efficiency\n");
+				lev--;
+			}
+			max_lev = lev;
+		}
+		part[lev] = cur;
+	}
+
+	for (lev = 0; lev < max_lev; lev++)
+		if (part[lev])
+			list = merge(priv, cmp, part[lev], list);
+
+	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
+}
+EXPORT_SYMBOL(list_sort);
diff --git a/xen/include/xen/list_sort.h b/xen/include/xen/list_sort.h
new file mode 100644
index 0000000000..13ce0a55ec
--- /dev/null
+++ b/xen/include/xen/list_sort.h
@@ -0,0 +1,11 @@ 
+#ifndef _LINUX_LIST_SORT_H
+#define _LINUX_LIST_SORT_H
+
+#include <xen/types.h>
+
+struct list_head;
+
+void list_sort(void *priv, struct list_head *head,
+	       int (*cmp)(void *priv, struct list_head *a,
+			  struct list_head *b));
+#endif