Date: Mon, 14 Aug 2006 21:00:54 +0200 From: "Attilio Rao" <attilio@freebsd.org> To: freebsd-arch@freebsd.org, freebsd-current@freebsd.org, "John Baldwin" <jhb@freebsd.org> Subject: Re: [PATCH] Adding Solaris-style "owner of records" to rwlocks Message-ID: <3bbf2fe10608141200v51d370cajfde0fd94cf92aac@mail.gmail.com> In-Reply-To: <3bbf2fe10608071227j17c4cfa6qd84e1d8e53668fda@mail.gmail.com> References: <3bbf2fe10608071227j17c4cfa6qd84e1d8e53668fda@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
2006/8/7, Attilio Rao <attilio@freebsd.org>: > This is a first implementation of the owner of records concept in rwlocks. > It allows to avoid the priority inversion problem in the current > rwlocks implementation (for readers). > > The main idea (that John and I discussed) is to have as owner of > records the first rlock'er for a "class contention". > The implementation consists in adding two flags (RW_LOCK_OWNED and > RW_LOCK_EXEMPTED) which are used in order to not penalyze the easy > case, and syncronizing the operation of acquiring and dropping the > owner of records with the turnstile spin-lock. > The main scheme might work in this way: > > thread1::rlock() -> sets the owner of records > thread2::rlock() -> checks for RW_LOCK_OWNED bit and, if it is set, go > in the easy case > thread3::rlock() -> checks for RW_LOCK_OWNED... > thread4::wlock() -> blocks and land its priority to thread1 > thread1::runlock() -> disable the owner of records (disowning the > associated turnstile) and sets the RW_LOCK_EXEMPTED flag. In this way > other threads will treact as an easy case. > ... > > What I actually need is a testing suite for heavy-load contentions, > since I would like to detect eventual races I missed, etc. If somebody > has a get-ready testing suite, please, let me know. > > The patch against HEAD is here: > http://users.gufi.org/~rookie/works/patches/rwlocks.diff > > Please, this is not intended to be a final implementation for this, > since I think that it can be improved; it is just a starting point for > ongoing works and improvements. I cleaned a lot the code, added some extra debug stubs and comments and get rid of RW_LOCK_EXEMPTED bit. Please refer to: http://users.gufi.org/~rookie/works/patches/rwlocks2.diff in order to make tests and comments. Thanks, Attilio -- Peace can only be achieved by understanding - A. Einstein
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3bbf2fe10608141200v51d370cajfde0fd94cf92aac>