Date: Sat, 24 Nov 2007 04:30:29 +0100 From: "Attilio Rao" <attilio@freebsd.org> To: "Robert Watson" <rwatson@freebsd.org> Cc: Stephan Uphoff <ups@freebsd.org>, Max Laier <max@love2party.net>, Alfred Perlstein <alfred@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: rwlocks, correctness over speed. Message-ID: <3bbf2fe10711231930m459dc800wbbb894b9fd50ca13@mail.gmail.com> In-Reply-To: <20071123235346.E14018@fledge.watson.org> References: <20071121222319.GX44563@elvis.mu.org> <200711221641.02484.max@love2party.net> <3bbf2fe10711220753u435ff4cbxa94d5b682292b970@mail.gmail.com> <200711221726.27108.max@love2party.net> <20071123082339.GN44563@elvis.mu.org> <47469328.8020404@freebsd.org> <20071123092415.GP44563@elvis.mu.org> <4746F858.4070301@freebsd.org> <20071123235346.E14018@fledge.watson.org>
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2007/11/24, Robert Watson <rwatson@freebsd.org>: > While I'm no great fan of recursion, the reality is that many of our kernel > subsystems are not yet ready to disallow recursion on locks. Take a look at > the cases where we explicitly enable recursive acquisition for mutexes--in > practice, most network stack mutexes are recursive due to the recursive > calling in the network stack. While someday I'd like to think we'll be able > to eliminate some of that, but it won't be soon since it requires significant > reworking of very complicated code. The current model in which recursion is > explicitly enabled only where still required seems to work pretty well for the > existing code, although it's hard to say yet in the code I've looked at > whether read recursion would be required--the situations I have in mind would > require purely write recursion. There's one case in the UNIX domain socket > code where we do a locked test and conditional lock/unlock with an rwlock for > exclusive locking because recursion isn't currently supported, and that's not > a usage I'd like to encourage more of. Oh, I just didn't notice this -- rwlock are only present in 7.0 and in 7.0 they support recursion in exclusive mode, so I'm not sure what do you mean with 'recursion isn't currently supported'. Thanks, Attilio -- Peace can only be achieved by understanding - A. Einstein
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