when translating descriptors they are typically less than
memory region that holds them and translated into 1 iov
entry, so it's not nessesary to check remaining length
twice and calculate used length and next address
in such cases.

replace a remaining length and 'size' increment branches
with a single remaining length check and execute
next iov steps only when it needed.

It saves a tiny 2% of translate_desc() execution time.

Signed-off-by: Igor Mammedov <imamm...@redhat.com>
---
PS:
I'm not sure if iov_size > 0 is always true, if it's not
then better to drop this patch.
---
 drivers/vhost/vhost.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 5c39a1e..5bcb323 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1111,12 +1111,8 @@ static int translate_desc(struct vhost_virtqueue *vq, 
u64 addr, u32 len,
        int ret = 0;
 
        mem = vq->memory;
-       while ((u64)len > s) {
+       do {
                u64 size;
-               if (unlikely(ret >= iov_size)) {
-                       ret = -ENOBUFS;
-                       break;
-               }
                reg = find_region(mem, addr, len, &vq->cached_reg);
                if (unlikely(!reg)) {
                        ret = -EFAULT;
@@ -1124,13 +1120,22 @@ static int translate_desc(struct vhost_virtqueue *vq, 
u64 addr, u32 len,
                }
                _iov = iov + ret;
                size = reg->memory_size - addr + reg->guest_phys_addr;
-               _iov->iov_len = min((u64)len - s, size);
                _iov->iov_base = (void __user *)(unsigned long)
                        (reg->userspace_addr + addr - reg->guest_phys_addr);
+               ++ret;
+               if (likely((u64)len - s < size)) {
+                       _iov->iov_len = (u64)len - s;
+                       break;
+               }
+
+               if (unlikely(ret >= iov_size)) {
+                       ret = -ENOBUFS;
+                       break;
+               }
+               _iov->iov_len = size;
                s += size;
                addr += size;
-               ++ret;
-       }
+       } while (1);
 
        return ret;
 }
-- 
1.8.3.1

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Reply via email to