Date: Fri, 16 Aug 2013 10:16:03 +0200 From: Jeremie Le Hen <jlh@FreeBSD.org> To: Alexander Motin <mav@FreeBSD.org> Cc: Scott Long <scottl@FreeBSD.org>, Jeff Roberson <jeff@freebsd.org>, ken <ken@freebsd.org>, freebsd-hackers@FreeBSD.org, FreeBSD SCSI <freebsd-scsi@freebsd.org>, Steven Hartland <smh@FreeBSD.org>, "Justin T. Gibbs" <gibbs@FreeBSD.org> Subject: Re: New CAM locking preview Message-ID: <20130816081603.GA4984@caravan.chchile.org> In-Reply-To: <520D4ADB.50209@FreeBSD.org> References: <520D4ADB.50209@FreeBSD.org>
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On Fri, Aug 16, 2013 at 12:40:43AM +0300, Alexander Motin wrote: > Hi. > > Last weeks I've made substantial progress on my CAM locking work. In > fact, at this moment I think I've tied all loose ends good enough to > consider the new design viable and implementation worth further testing > and bug fixing. So I would like to ask for review of my work from > everybody who interested in CAM internals. > > In short, my idea was to split single per-SIM lock, that creates huge > congestion under high IOPS, into several smaller ones. So design I've > finally chosen includes such locks: > 1) New per-device (per-LUN) locks to protect state of the devices and > respective periphs. In most cases peripheral drivers just use that lock > instead of SIM lock used before, so code modification is minimal and > straightforward. > 2) New per-target lock to protect list of LUNs fetched from the device. > 3) Old single per-SIM lock to protect SIM driver internals, but only > that. No parts of CAM itself use that lock. Keeping it for SIMs allows > to keep API and hopefully ABI compatibility. Reducing its scope allows > to reduce congestion. > 4) New per-SIM lock to protect SIM and device command queues. That > allows execute queued commands from any context unrelated to other > locks. Also this lock serializes accesses to sim_action() method for the > most of commands, this allows to mostly avoid busy spilling on SIM lock > collision. > 5) New per-bus locks to protect target, device and periphs reference > counters. It allows to create and destroy paths unrelated to other locks > in any possible context. > > Numbers above also define supposed lock ordering: while holding > per-device lock 1) is allowed to request SIM lock 3), but not backward. > Cases where opposite is required (command completions and async events) > are handled via queuing events via several completion threads. The rest > of locks are self-contained and does not really suppose cascading. > > All these changes combined with GEOM direct dispatch (it will be next > separate project) allow to double system performance in disk I/O > microbenchmarks, comparing to present head, same as it was announced on > 2013-05 DevSummit: http://people.freebsd.org/~mav/camlock.pdf . Tests > without GEOM changes also show performance improvement, but limited by > heavy bottleneck at the GEOM g_up/g_down threads at the level of 5-20%. > > Project sources could be found at SVN projects/camlock branch: > http://svnweb.freebsd.org/base/projects/camlock/ . Many early changes > from that branch are already integrated to head, so to simplify review > the rest patches for changes before r254059 were manually remade and > could be found here: http://people.freebsd.org/~mav/camlock_patches/ . > > These changes do not require controller driver modifications, keeping > KPIs and hopefully KBIs intact, but create base for later work to use > multiqueue capabilities of new controllers. > > This work is sponsored by iXsystems, Inc. Excellent, thanks to both you and iXsystems. I'm eager to see everything merged to -CURRENT before the code slush ;). -- Jeremie Le Hen Scientists say the world is made up of Protons, Neutrons and Electrons. They forgot to mention Morons.
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