Date: Thu, 15 Aug 2013 18:12:05 -0700 From: Adrian Chadd <adrian@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-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: <CAJ-VmonD_MJSdc6M_H14k-nWotg1cN1GG1=U7B2OtOnhGDn02g@mail.gmail.com> In-Reply-To: <520D4ADB.50209@FreeBSD.org> References: <520D4ADB.50209@FreeBSD.org>
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Cool! I assume you've run this with full witness debugging enabled, to catch lock ordering issues? This is great. I look forward to per-CPU, pinned, completion threads that I can do interesting things with (like schedule aio-sendfile completions..) -adrian On 15 August 2013 14:40, Alexander Motin <mav@freebsd.org> 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<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/<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/ <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. > > -- > Alexander Motin > ______________________________**_________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/**mailman/listinfo/freebsd-**hackers<http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>; > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@** > freebsd.org <freebsd-hackers-unsubscribe@freebsd.org>" >
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