Improve qemu-nbd performance by 4400 %
This patch allows to reduce the boot time from an NBD server from 225 seconds to
5 seconds (time between the "boot cd:0" and the kernel init) for the
following command lines:
./qemu-nbd -t ../ISO/debian-500-powerpc-netinst.iso
and
./ppc-softmmu/qemu-system-ppc -cdrom nbd:localhost:1024
This patch combines the reply header and payload send operation.
Signed-off-by: Laurent Vivier <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>
diff --git a/nbd.c b/nbd.c
index 011b50f..4bf2eb7 100644
--- a/nbd.c
+++ b/nbd.c
@@ -49,6 +49,7 @@
/* This is all part of the "official" NBD API */
+#define NBD_REPLY_SIZE (4 + 4 + 8)
#define NBD_REQUEST_MAGIC 0x25609513
#define NBD_REPLY_MAGIC 0x67446698
@@ -588,7 +589,7 @@
int nbd_receive_reply(int csock, struct nbd_reply *reply)
{
- uint8_t buf[4 + 4 + 8];
+ uint8_t buf[NBD_REPLY_SIZE];
uint32_t magic;
memset(buf, 0xAA, sizeof(buf));
@@ -655,9 +656,9 @@
if (nbd_receive_request(csock, &request) == -1)
return -1;
- if (request.len > data_size) {
+ if (request.len + NBD_REPLY_SIZE > data_size) {
LOG("len (%u) is larger than max len (%u)",
- request.len, data_size);
+ request.len + NBD_REPLY_SIZE, data_size);
errno = EINVAL;
return -1;
}
@@ -687,7 +688,8 @@
case NBD_CMD_READ:
TRACE("Request type is READ");
- if (bdrv_read(bs, (request.from + dev_offset) / 512, data,
+ if (bdrv_read(bs, (request.from + dev_offset) / 512,
+ data + NBD_REPLY_SIZE,
request.len / 512) == -1) {
LOG("reading from file failed");
errno = EINVAL;
@@ -697,12 +699,21 @@
TRACE("Read %u byte(s)", request.len);
- if (nbd_send_reply(csock, &reply) == -1)
- return -1;
+ /* Reply
+ [ 0 .. 3] magic (NBD_REPLY_MAGIC)
+ [ 4 .. 7] error (0 == no error)
+ [ 7 .. 15] handle
+ */
+
+ cpu_to_be32w((uint32_t*)data, NBD_REPLY_MAGIC);
+ cpu_to_be32w((uint32_t*)(data + 4), reply.error);
+ cpu_to_be64w((uint64_t*)(data + 8), reply.handle);
TRACE("Sending data to client");
- if (write_sync(csock, data, request.len) != request.len) {
+ if (write_sync(csock, data,
+ request.len + NBD_REPLY_SIZE) !=
+ request.len + NBD_REPLY_SIZE) {
LOG("writing to socket failed");
errno = EINVAL;
return -1;
