On Mon, Jun 30, 2014 at 01:04:09PM +0200, Michal Skrivanek wrote:
Hi, just thinking about the recent stats hook[1] by Dima and scale, It is a very nice hook and quite useful for the scale testing - ( though when focus is on engine I'd suggest to use FakeVDSM instead to eliminate all the bottlenecks on VDSM side.)
One issue I see - since this is a very high-profile call, every 15s time number of VMs - is with the hook invocation. Currently the hook mechanism always go through the hooks dit and does stat() call to see script is there or not… it certainly doesn't matter on small scale but when the system is on the edge every IO on local FS cost something….
Would be nice if the hook mechanism is enhanced in general, figure out which hooks are relevant only at the startup and don't waste time passing domainXML every single time when the hook is not there
But a caching mechanism for hook scripts costs "something", too (code size, bugs, simplicty of testing new script). Before complicating the mechanism, I'd rather see numbers: how much would be saved? I would guess that filesystem caching already shaves costs of stat()s. Writing domxml to a memory-map file before starting a vm may be insignificant, too. Dan.