Re: rw_lock vs mutex
On Feb 2, 2012, at 5:38 PM, Paul Goyette wrote: While digging around looking into another problem, I noticed that the piixpm(4) driver uses an rw_lock for its ic_acquire_bus/ic_release_bus routines. ic_acquire_bus() uses rw_enter(..., RW_WRITER) and there doesn't appear to be any use anywhere of RW_READER for that lock. The man page for rw_lock implies that it is a superset of a mutex. So I'm wondering if it makes any sense to use the simpler mutex instead? Switch to a mutex, it's much less overhead that a r/w lock
RE: rw_lock vs mutex
A rw_lock allows multiple readers, correct? If there's a non-trivial probability of concurrent reads that would make a difference. If not, then a mutex would be just as good especially if that is lower overhead. paul -Original Message- From: tech-kern-ow...@netbsd.org [mailto:tech-kern-ow...@netbsd.org] On Behalf Of Matt Thomas Sent: Thursday, February 02, 2012 8:53 PM To: p...@whooppee.com Cc: tech-kern@netbsd.org Subject: Re: rw_lock vs mutex On Feb 2, 2012, at 5:38 PM, Paul Goyette wrote: While digging around looking into another problem, I noticed that the piixpm(4) driver uses an rw_lock for its ic_acquire_bus/ic_release_bus routines. ic_acquire_bus() uses rw_enter(..., RW_WRITER) and there doesn't appear to be any use anywhere of RW_READER for that lock. The man page for rw_lock implies that it is a superset of a mutex. So I'm wondering if it makes any sense to use the simpler mutex instead? Switch to a mutex, it's much less overhead that a r/w lock
RE: rw_lock vs mutex
On Thu, 2 Feb 2012, paul_kon...@dell.com wrote: A rw_lock allows multiple readers, correct? If there's a non-trivial probability of concurrent reads that would make a difference. If not, then a mutex would be just as good especially if that is lower overhead. The rwlock in question is contained with the driver's softc. The only exported accessors are i2c_bus_acquire() (which grabs a RW_WRITER lock) and i2c_bus_release(). A mutex makes much more sense. - | Paul Goyette | PGP Key fingerprint: | E-mail addresses: | | Customer Service | FA29 0E3B 35AF E8AE 6651 | paul at whooppee.com| | Network Engineer | 0786 F758 55DE 53BA 7731 | pgoyette at juniper.net | | Kernel Developer | | pgoyette at netbsd.org | -
