perf: simple setup upstream

[tzssangglass]

Description

Fixes # (issue)

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[spacewander]

We can move:

if enable_keepalive then

to here?
Like:

if enable_keepalive then
    balancer.enable_keepalive(60, 1000)

[tzssangglass]

maybe not, follow:

apisix/apisix/balancer.lua

Lines 291 to 338 in ecdc209

	if enable_keepalive then
	if not keepalive_pool then
	if not default_keepalive_pool then
	local local_conf = core.config.local_conf()
	local up_keepalive_conf =
	core.table.try_read_attr(local_conf, "nginx_config",
	"http", "upstream")
	default_keepalive_pool = {}
	default_keepalive_pool.idle_timeout =
	core.config_util.parse_time_unit(up_keepalive_conf.keepalive_timeout)
	default_keepalive_pool.size = up_keepalive_conf.keepalive
	default_keepalive_pool.requests = up_keepalive_conf.keepalive_requests
	end
	keepalive_pool = default_keepalive_pool
	end
	local idle_timeout = keepalive_pool.idle_timeout
	local size = keepalive_pool.size
	local requests = keepalive_pool.requests
	core.table.clear(pool_opt)
	pool_opt.pool_size = size
	local scheme = up_conf.scheme
	-- other TLS schemes don't use http balancer keepalive
	if (scheme == "https" or scheme == "grpcs") then
	local pool = server.host .. "#" .. server.port
	local sni = ctx.var.upstream_host
	pool = pool .. "#" .. sni
	if up_conf.tls and up_conf.tls.client_cert then
	pool = pool .. "#" .. up_conf.tls.client_cert
	end
	pool_opt.pool = pool
	end
	local ok, err = balancer.set_current_peer(server.host, server.port,
	pool_opt)
	if not ok then
	return ok, err
	end
	return balancer.enable_keepalive(idle_timeout, requests)
	end
	return balancer.set_current_peer(server.host, server.port)

if enable_keepalive, would add pool_opt as the third argument to balancer.set_current_peer.

Do we fix the call to set_current_peer here and in balancer.lua, pass pool_opt even if there is disable enable_keepalive, otherwise it will all become non-persistent connection.