[PATCH v6 3/4] xen/console: use memcpy() in console_init_ring()

[dmukhin@xxxxxxxx]

From: Denis Mukhin <dmukhin@xxxxxxxx> 

Make console_init_ring() more efficient by using memcpy()'s, rather than
copying the ring a byte at a time.

Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes since v5:
- fixed memcpy() logic
---
 xen/drivers/char/console.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 5ab3b0de12d8..5cac87d052b9 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -463,7 +463,8 @@ static void cf_check conring_dump_keyhandler(unsigned char 
key)
 void __init console_init_ring(void)
 {
     char *ring;
-    unsigned int i, order, memflags;
+    XENCONS_RING_IDX i, size;
+    unsigned int order, memflags;
     unsigned long flags;
 
     if ( !opt_conring_size )
@@ -479,8 +480,22 @@ void __init console_init_ring(void)
     opt_conring_size = PAGE_SIZE << order;
 
     nrspin_lock_irqsave(&console_lock, flags);
-    for ( i = conringc ; i != conringp; i++ )
-        ring[i & (opt_conring_size - 1)] = conring[i & (conring_size - 1)];
+
+    i = 0;
+    size = conringp - conringc;
+    while ( i < size )
+    {
+        XENCONS_RING_IDX src = (conringc + i) & (conring_size - 1);
+        XENCONS_RING_IDX dst = (conringc + i) & (opt_conring_size - 1);
+        XENCONS_RING_IDX n;
+
+        n = min(opt_conring_size - dst, conring_size - src);
+        n = min(size - i, n);
+
+        memcpy(&ring[dst], &conring[src], n);
+        i += n;
+    }
+
     conring = ring;
     smp_wmb(); /* Allow users of console_force_unlock() to see larger buffer. 
*/
     conring_size = opt_conring_size;
-- 
2.54.0