Subject: Re: [PATCH] fetch-pack: grow stateless RPC windows exponentially

From: Junio C Hamano <[email-masked]>
Date: Mon, 18 Jul 2016 13:00:41 -0700

Jonathan Nieder <[email-masked]> writes:

> You have full control of the growth function.  So how about aggressive
> growth until 1024*10?
>
> That is:
>
> Current git:
>   n < 1024: aggressive exponential
> 	16, 32, 64, 128, 256, 512, 1024
>   1024 <= n: linear
> 	2048, 3072, 4096, 5120, ...
>
> Initial proposal:
>   n < 1024: aggressive exponential
> 	16, 32, 64, 128, 256, 512, 1024
>   1024 <= n < 10240: linear
> 	2048, 307, 4096, 5120, ...
>   10240 <= n: conservative exponential
> 	11264, 12390, ...
>
> New proposal:
>   n < 10240: aggressive exponential
> 	16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384
>   10240 <= n: conservative exponential
> 	18022, 19824, ...
>
> That way, on one hand it would still never use a smaller window than
> today and on the other hand the heuristic would be easier to
> understand (only decelarating, instead of decelarating and then
> accelerating again).

That sounds more explainable (I do not know if that is a growth
curve that gives us better results, though).

So, the result would look something like this, perhaps?

 fetch-pack.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fetch-pack.c b/fetch-pack.c
index 3c5dfc4..97fe5f7 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -264,12 +264,17 @@ static void insert_one_alternate_ref(const struct ref *ref, void *unused)
 
 static int next_flush(struct fetch_pack_args *args, int count)
 {
-	int flush_limit = args->stateless_rpc ? LARGE_FLUSH : PIPESAFE_FLUSH;
-
-	if (count < flush_limit)
-		count <<= 1;
-	else
-		count += flush_limit;
+	if (args->stateless_rpc) {
+		if (count < LARGE_FLUSH * 10)
+			count <<= 1;
+		else
+			count = count * 11 / 10;
+	} else {
+		if (count < PIPESAFE_FLUSH)
+			count <<= 1;
+		else
+			count += PIPESAFE_FLUSH;
+	}
 	return count;
 }