[sheepdog] [PATCH] sheep: stop special casing local objects on gateways

[MORITA Kazutaka]

At Wed, 06 Jun 2012 18:52:16 +0800,
Liu Yuan wrote:
> 
> On 06/06/2012 06:44 PM, Christoph Hellwig wrote:
> 
> > On Wed, Jun 06, 2012 at 11:56:53AM +0800, Liu Yuan wrote:
> >> The pros is simplification of code, but you don't say cons, I think we
> >> should know the perf number we lost by adding a network overhead for IOs
> >> happen to be local, this can be easily collected by built-in tracer.
> > 
> > What kind of setup do you want to see this on, e.g. what number of
> > nodes?
> > 
> 
> 
> At your convenience :) Maybe two (small cluster and bigger one) would
> suffice. With cached FD pool, we might not lose that much performance
> for a quick thought, though, but this is quite radical change of design,
> numbers will definitely help it in. Kazum, how do you think of this change?

I like the idea to remove object I/Os in the gateway worker threads.

How about something like the following change on top of the Christoph
patch?  It still has a socket overhead, but the gateway can read
objects from local if they are available.


diff --git a/sheep/gateway.c b/sheep/gateway.c
index 8b7777c..1124f8d 100644
--- a/sheep/gateway.c
+++ b/sheep/gateway.c
@@ -24,6 +24,7 @@ int forward_read_obj_req(struct request *req)
 	struct sd_rsp *rsp = (struct sd_rsp *)&fwd_hdr;
 	uint64_t oid = req->rq.obj.oid;
 	int nr_copies, j;
+	struct sd_vnode *obj_vnodes[SD_MAX_COPIES];
 
 	memcpy(&fwd_hdr, &req->rq, sizeof(fwd_hdr));
 	fwd_hdr.flags |= SD_FLAG_CMD_IO_LOCAL;
@@ -37,6 +38,16 @@ int forward_read_obj_req(struct request *req)
 	 * reading base VM's COW objects
 	 */
 	j = random();
+
+	/* Read from local if possible */
+	oid_to_vnodes(req->vnodes, oid, nr_copies, obj_vnodes);
+	for (i = 0; i < nr_copies; i++) {
+		if (vnode_is_local(obj_vnodes[i])) {
+			j = i;
+			break;
+		}
+	}
+
 	for (i = 0; i < nr_copies; i++) {
 		int idx = (i + j) % nr_copies;
 		struct sd_vnode *v = oid_to_vnode(req->vnodes, oid, idx);