From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Teigland Date: Fri, 4 Nov 2011 12:31:52 -0400 Subject: [Cluster-devel] GFS2: glock statistics gathering (RFC) In-Reply-To: <1320419989.2732.60.camel@menhir> References: <1320419989.2732.60.camel@menhir> Message-ID: <20111104163152.GA15232@redhat.com> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, Nov 04, 2011 at 03:19:49PM +0000, Steven Whitehouse wrote: > The three pairs of mean/variance measure the following > things: > > 1. DLM lock time (non-blocking requests) You don't need to track and save this value, because all results will be one of three values which can gather once: short: the dir node and master node are local: 0 network round trip medium: one is local, one is remote: 1 network round trip long: both are remote: 2 network round trips Once you've measured values for short/med/long, then you're done. The distribution will depend on the usage pattern. > 2. DLM lock time (blocking requests) I think what you want to quantify is how much contention a given lock is under. A time measurement is probably not a great way to get that since it's a combination of: the value above, how long gfs2 takes to release the lock (itself a combination of things, including the the tunable itself), and how many nodes are competing for the lock (depends on workload). > 3. Inter-request time (again to the DLM) Time between gfs2 requesting the same lock? That sounds like it might work ok for measuring contention. > 1. To be able to better set the glock "min hold time" Less for a lock with high contention? > 2. To spot performance issues more easily Apart from contention, I'm not sure there are many perf issues that dlm measurements would help with. > 3. To improve the algorithm for selecting resource groups for > allocation (to base it on lock wait time, rather than blindly > using a "try lock") Don't you grab an rg lock and keep it cached? How would lock times help? Also, ocfs2 keeps quite a lot of locking stats you might look at. Dave