[PATCH] vfio/migration: Improve to read/write full migration region per chunk

[Yishai Hadas]

Upon reading/writing the migration data there is no real reason to limit
the read/write system call from the file to be 8 bytes.

In addition, there is no reason to depend on the file offset alignment.
The offset is just some logical value which depends also on the region
index and has nothing to do with the amount of data that can be
accessed.

Move to read/write the full region size per chunk, this reduces
dramatically the number of the systems calls that are needed and improve
performance.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
---
 hw/vfio/migration.c | 36 ++----------------------------------
 1 file changed, 2 insertions(+), 34 deletions(-)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index ff6b45de6b5..b5f310bb831 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -62,40 +62,8 @@ static inline int vfio_mig_access(VFIODevice *vbasedev, void 
*val, int count,
     return 0;
 }
 
-static int vfio_mig_rw(VFIODevice *vbasedev, __u8 *buf, size_t count,
-                       off_t off, bool iswrite)
-{
-    int ret, done = 0;
-    __u8 *tbuf = buf;
-
-    while (count) {
-        int bytes = 0;
-
-        if (count >= 8 && !(off % 8)) {
-            bytes = 8;
-        } else if (count >= 4 && !(off % 4)) {
-            bytes = 4;
-        } else if (count >= 2 && !(off % 2)) {
-            bytes = 2;
-        } else {
-            bytes = 1;
-        }
-
-        ret = vfio_mig_access(vbasedev, tbuf, bytes, off, iswrite);
-        if (ret) {
-            return ret;
-        }
-
-        count -= bytes;
-        done += bytes;
-        off += bytes;
-        tbuf += bytes;
-    }
-    return done;
-}
-
-#define vfio_mig_read(f, v, c, o)       vfio_mig_rw(f, (__u8 *)v, c, o, false)
-#define vfio_mig_write(f, v, c, o)      vfio_mig_rw(f, (__u8 *)v, c, o, true)
+#define vfio_mig_read(f, v, c, o)       vfio_mig_access(f, (__u8 *)v, c, o, 
false)
+#define vfio_mig_write(f, v, c, o)      vfio_mig_access(f, (__u8 *)v, c, o, 
true)
 
 #define VFIO_MIG_STRUCT_OFFSET(f)       \
                                  offsetof(struct vfio_device_migration_info, f)
-- 
2.18.1