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nbd: improve CMD_CACHE: use BDRV_REQ_PREFETCH 

This helps to avoid extra io, allocations and memory copying.
We assume here that CMD_CACHE is always used with copy-on-read, as
otherwise it's a noop.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20190725100550.33801-4-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2019-07-25 13:05:50 +03:00 committed by Eric Blake
parent 99136607b1
commit 7fa5c5657f
1 changed files with 35 additions and 8 deletions
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43
nbd/server.c
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@ -2104,12 +2104,15 @@ static int nbd_co_receive_request(NBDRequestData *req, NBDRequest *request,
return -EINVAL;
}
req->data = blk_try_blockalign(client->exp->blk, request->len);
if (req->data == NULL) {
error_setg(errp, "No memory");
return -ENOMEM;
if (request->type != NBD_CMD_CACHE) {
req->data = blk_try_blockalign(client->exp->blk, request->len);
if (req->data == NULL) {
error_setg(errp, "No memory");
return -ENOMEM;
}
}
}
if (request->type == NBD_CMD_WRITE) {
if (nbd_read(client->ioc, req->data, request->len, "CMD_WRITE data",
errp) < 0)
@ -2194,7 +2197,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
int ret;
NBDExport *exp = client->exp;
assert(request->type == NBD_CMD_READ || request->type == NBD_CMD_CACHE);
assert(request->type == NBD_CMD_READ);
/* XXX: NBD Protocol only documents use of FUA with WRITE */
if (request->flags & NBD_CMD_FLAG_FUA) {
@ -2206,7 +2209,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
}
if (client->structured_reply && !(request->flags & NBD_CMD_FLAG_DF) &&
request->len && request->type != NBD_CMD_CACHE)
request->len)
{
return nbd_co_send_sparse_read(client, request->handle, request->from,
data, request->len, errp);
@ -2214,7 +2217,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
ret = blk_pread(exp->blk, request->from + exp->dev_offset, data,
request->len);
if (ret < 0 || request->type == NBD_CMD_CACHE) {
if (ret < 0) {
return nbd_send_generic_reply(client, request->handle, ret,
"reading from file failed", errp);
}
@ -2233,6 +2236,28 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
}
}
/*
* nbd_do_cmd_cache
*
* Handle NBD_CMD_CACHE request.
* Return -errno if sending fails. Other errors are reported directly to the
* client as an error reply.
*/
static coroutine_fn int nbd_do_cmd_cache(NBDClient *client, NBDRequest *request,
Error **errp)
{
int ret;
NBDExport *exp = client->exp;
assert(request->type == NBD_CMD_CACHE);
ret = blk_co_preadv(exp->blk, request->from + exp->dev_offset, request->len,
NULL, BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH);
return nbd_send_generic_reply(client, request->handle, ret,
"caching data failed", errp);
}
/* Handle NBD request.
* Return -errno if sending fails. Other errors are reported directly to the
* client as an error reply. */
@ -2246,8 +2271,10 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
char *msg;
switch (request->type) {
case NBD_CMD_READ:
case NBD_CMD_CACHE:
return nbd_do_cmd_cache(client, request, errp);
case NBD_CMD_READ:
return nbd_do_cmd_read(client, request, data, errp);
case NBD_CMD_WRITE: