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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 <laurent@vivier.eu>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Laurent Vivier 2010-09-17 18:13:57 +02:00 committed by Kevin Wolf
parent 581b9e29f3
commit 5fe16888d3
1 changed files with 18 additions and 7 deletions
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25
nbd.c
View File

@ -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 @@ static int nbd_receive_request(int csock, struct nbd_request *request)
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 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
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 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
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 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
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;