Date: Tue, 24 Apr 2001 11:45:07 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: Barney Wolff <barney@databus.com> Cc: smp@FreeBSD.org, Robert Watson <rwatson@FreeBSD.org>, "Andrew R. Reiter" <arr@watson.org> Subject: Re: sysctl's and mutexes Message-ID: <XFMail.010424114507.jhb@FreeBSD.org> In-Reply-To: <20010424135845.A10320@mx.databus.com>
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On 24-Apr-01 Barney Wolff wrote: > Pardon an outsider's question, but what exactly are these mutex's > supposed to protect? Would a reader of a sysctl value have to > acquire a read lock in order to read a non-atomic value? > > Is the rate at which these values are set and/or read so high > as to justify more than a single mutex for the lot? Are there > any operations that take long enough that anything other than > a spinlock is justified? > > Sorry if these are dumb questions - I'm just a KISS sort of guy. If a user is using a sysctl to read/write a variable that we protect with a given lock inside the kernel, we need to use that same lock to protect the data in the sysctl handler. Granted, for some read-only sysctl's, it could be perfectly fine to not grab a lock while performing the sysctl. The trick though is that you always need to use the same locks to protect a given piece of data. -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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