Date: Sat, 24 Jan 2009 19:56:43 -0800 From: Kip Macy <kmacy@freebsd.org> To: Julian Elischer <julian@elischer.org> Cc: arch@freebsd.org Subject: Re: need for another mutex type/flag? Message-ID: <3c1674c90901241956j244ed067p7ff4df5454beba82@mail.gmail.com> In-Reply-To: <497BA91D.805@elischer.org> References: <497BA91D.805@elischer.org>
next in thread | previous in thread | raw e-mail | index | archive | help
The adaptive spinning of regular mutexes already satisfies your need for "short" hold. You might wish to add a thread flag used when INVARIANTS is enabled that is set when a leaf mutex is acquired and checked on all mutex acquisitions. -Kip On Sat, Jan 24, 2009 at 3:49 PM, Julian Elischer <julian@elischer.org> wrote: > Currently we have: > spin locks.. > you really don't want to hold these for > any time at all, and this is enforced to some extent in the waiter. > > regular mutexes.. > You can hold these for as long as you want but teh shorter > the better and you can't sleep when holding them. The > "shortness" of the time of holding the mutex is not enforced. > > "Sleeps" (including sx-locks and friends) > You may hold these or be descheduled for really long periods of time. > > > Now it occurs to me that there is a subclass of regular mutexes, > usage, which is where you want to use a mutex to guard some small > but critical structure, and that you know that access to that structure will > be quick, and that you can guarantee that you will > not acquire any other locks (which could introduce unknown delay) > while hoding the lock. > > One way of thinking about this is that this lock would always be > a leaf node on the tree of lock orders. > I would like to be able to add a flag to a mutex > that tags it as a 'leaf' mutex. As a result it would be illegal > to take any other mutex while holding a leaf mutex. Somewhat > similar to the way that it is illegal to take aregular > mutex while holding a spin mutex.. > > > In netgraph I have a stipulation that is hard to specify which > is that you MAY take a mutex in a netgraph node if you can guarantee > that the mutex WILL be satisfied very quickly, but it'd > be nice to be able to specify "you may only take 'leaf' mutexes within an > netgraph node". > > > thoughts? (especially from jhb and other locking types). > > > _______________________________________________ > freebsd-arch@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org" >
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3c1674c90901241956j244ed067p7ff4df5454beba82>