Hi Shanker,
On 27/06/16 21:33, Shanker Donthineni wrote:
As the number of I/O handlers increase, the overhead associated with
linear lookup also increases. The system might have maximum of 144
(assuming CONFIG_NR_CPUS=128) mmio handlers. In worst case scenario,
it would require 144 iterations for finding a matching handler. Now
it is time for us to change from linear (complexity O(n)) to a binary
search (complexity O(log n) for reducing mmio handler lookup overhead.
Signed-off-by: Shanker Donthineni <shank...@codeaurora.org>
---
Changes since v2:
Converted mmio lookup code to a critical section.
Copied the function bsreach() from Linux kernel.
xen/arch/arm/io.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 84 insertions(+), 13 deletions(-)
diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
index a5b2c2d..c31fdf3 100644
--- a/xen/arch/arm/io.c
+++ b/xen/arch/arm/io.c
@@ -20,9 +20,50 @@
#include <xen/lib.h>
#include <xen/spinlock.h>
#include <xen/sched.h>
+#include <xen/sort.h>
#include <asm/current.h>
#include <asm/mmio.h>
+/*
+ * bsearch - binary search an array of elements
+ * @key: pointer to item being searched for
+ * @base: pointer to first element to search
+ * @num: number of elements
+ * @size: size of each element
+ * @cmp: pointer to comparison function
+ *
+ * This function does a binary search on the given array. The
+ * contents of the array should already be in ascending sorted order
+ * under the provided comparison function.
+ *
+ * Note that the key need not have the same type as the elements in
+ * the array, e.g. key could be a string and the comparison function
+ * could compare the string with the struct's name field. However, if
+ * the key and elements in the array are of the same type, you can use
+ * the same comparison function for both sort() and bsearch().
+ */
+static void *bsearch(const void *key, const void *base, size_t num, size_t
size,
+ int (*cmp)(const void *key, const void *elt))
This function is not specific to I/O handlers. So this should be moved
to common code. Also please mention in the commit message where the code
came from.
+{
+ size_t start = 0, end = num;
+ int result;
+
+ while ( start < end )
+ {
+ size_t mid = start + (end - start) / 2;
+
+ result = cmp(key, base + mid * size);
+ if ( result < 0 )
+ end = mid;
+ else if ( result > 0 )
+ start = mid + 1;
+ else
+ return (void *)base + mid * size;
+ }
+
+ return NULL;
+}
+
static int handle_read(const struct mmio_handler *handler, struct vcpu *v,
mmio_info_t *info)
{
@@ -70,23 +111,41 @@ static int handle_write(const struct mmio_handler
*handler, struct vcpu *v,
handler->priv);
}
-int handle_mmio(mmio_info_t *info)
+static int match_mmio_handler(const void *key, const void *elem)
{
- struct vcpu *v = current;
- int i;
- const struct mmio_handler *handler = NULL;
- const struct vmmio *vmmio = &v->domain->arch.vmmio;
+ const struct mmio_handler *handler = elem;
+ paddr_t addr = (paddr_t)key;
- for ( i = 0; i < vmmio->num_entries; i++ )
- {
- handler = &vmmio->handlers[i];
+ if ( addr < handler->addr )
+ return -1;
- if ( (info->gpa >= handler->addr) &&
- (info->gpa < (handler->addr + handler->size)) )
- break;
- }
+ if ( addr > (handler->addr + handler->size) )
+ return 1;
+
+ return 0;
+}
- if ( i == vmmio->num_entries )
+static const struct mmio_handler *
+find_mmio_handler(struct vcpu *v, paddr_t addr)
+{
+ struct vmmio *vmmio = &v->domain->arch.vmmio;
+ const struct mmio_handler *handler;
+
+ spin_lock(&vmmio->lock);
+ handler = bsearch((const void *)addr, vmmio->handlers, vmmio->num_entries,
paddr_t is always 64-bit regardless the architecture (ARM64 vs ARM32).
So the cast will lead to a compilation error on ARM32.
Please try to at least compile test your patch with ARM64, ARM32 and x86
(when you touch common code).
Anyway, I would try to merge the two compare functions
(match_mmio_handler, cmp_mmio_handler) which have very similar behavior.
+ sizeof(*handler), match_mmio_handler);
+ spin_unlock(&vmmio->lock);
+
+ return handler;
+}
+
+int handle_mmio(mmio_info_t *info)
+{
+ const struct mmio_handler *handler;
+ struct vcpu *v = current;
+
+ handler = find_mmio_handler(v, info->gpa);
+ if ( !handler )
return 0;
if ( info->dabt.write )
@@ -95,6 +154,14 @@ int handle_mmio(mmio_info_t *info)
return handle_read(handler, v, info);
}
+static int cmp_mmio_handler(const void *key, const void *elem)
+{
+ const struct mmio_handler *handler0 = key;
+ const struct mmio_handler *handler1 = elem;
+
+ return (handler0->addr < handler1->addr) ? -1 : 0;
+}
+
void register_mmio_handler(struct domain *d,
const struct mmio_handler_ops *ops,
paddr_t addr, paddr_t size, void *priv)
@@ -122,6 +189,10 @@ void register_mmio_handler(struct domain *d,
vmmio->num_entries++;
+ /* Sort mmio handlers in ascending order based on base address */
+ sort(vmmio->handlers, vmmio->num_entries, sizeof(struct mmio_handler),
+ cmp_mmio_handler, NULL);
+
spin_unlock(&vmmio->lock);
}
Regards,
--
Julien Grall
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
