[PATCH 1/4] libmultipath: path latency: fix default base num

From: Martin Wilck <mwilck@suse.com>
To: Christophe Varoqui <christophe.varoqui@opensvc.com>,
	Guan Junxiong <guanjunxiong@huawei.com>
Cc: dm-devel@redhat.com
Subject: [PATCH 1/4] libmultipath: path latency: fix default base num
Date: Sat, 18 Nov 2017 01:11:31 +0100	[thread overview]
Message-ID: <20171118001134.26622-2-mwilck@suse.com> (raw)
In-Reply-To: <20171118001134.26622-1-mwilck@suse.com>

I don't think anyone can measure latency to 1% accuracy. It's
better to not even pretend to be able to. 10% should be fine
even for the most latency-critical environments.

Signed-off-by: Martin Wilck <mwilck@suse.com>
---
 libmultipath/prioritizers/path_latency.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libmultipath/prioritizers/path_latency.c b/libmultipath/prioritizers/path_latency.c
index 9d5397ec1b3a..b8c5bc7c50a4 100644
--- a/libmultipath/prioritizers/path_latency.c
+++ b/libmultipath/prioritizers/path_latency.c
@@ -42,8 +42,9 @@
 #define DEF_IO_NUM		100
 
 #define MAX_BASE_NUM		10
-#define MIN_BASE_NUM		1.01
-#define DEF_BASE_NUM		1.5
+#define MIN_BASE_NUM		1.1
+// This is 10**(1/4). 4 prio steps correspond to a factor of 10.
+#define DEF_BASE_NUM		1.77827941004
 
 #define MAX_AVG_LATENCY		100000000.	/* Unit: us */
 #define MIN_AVG_LATENCY		1.		/* Unit: us */
-- 
2.15.0
