Date: Tue, 1 Jan 2008 16:37:22 +1100 (EST) From: Bruce Evans <brde@optusnet.com.au> To: "M. Warner Losh" <imp@bsdimp.com> Cc: rrs@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org, jhb@FreeBSD.org, cvs-src@FreeBSD.org Subject: Re: cvs commit: src/sys/netinet sctp_bsd_addr.c Message-ID: <20080101161858.A10345@delplex.bde.org> In-Reply-To: <20071231.203720.1306324107.imp@bsdimp.com> References: <200712291507.lBTF7sTA069010@repoman.freebsd.org> <200712311219.08286.jhb@freebsd.org> <20071231.203720.1306324107.imp@bsdimp.com>
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On Mon, 31 Dec 2007, M. Warner Losh wrote: > In message: <200712311219.08286.jhb@freebsd.org> > John Baldwin <jhb@FreeBSD.org> writes: > : The more correct fix though is to do a 'sched_prio()' at the start of the > : thread's main loop to set the priority and then not adjust it via msleep(). > : Kernel threads really should never pass a priority to msleep() but always '0' > : (which means "don't change my priority"). > > Not PZERO? When should one use PZERO and when should one use a bare > '0'? Can this information be added to the man page? PZERO is compatibility cruft which should never be used. Just a few places in kern still use it to invent a priority when no suitable priority (like PSOCK or PRIBIO) is already #defined. It isn't clear where these invented priorities are suitable. Otherwise, PZERO has a completely different meaning from either priority 0 (maximal) or the bare 0 arg to msleep. It means some middle priority, or the bias from priority 0 to get to that middle priority, so that after subtracting it, 0 becomes the middle priority. The bare 0 is actualy priority 0 (maximal) overloaded to mean "don't change the priority". This overloading doesn't lose anything except clarity since nothing is permitted to wake up at maximal priority after a sleep. (Maximal priority is reserved for realtime priority ithreads and even much lower priority ithreads are not permitted to sleep, and non-interrupt threads aren't permitted to run at ithread priorities except temporarily for priority propagation.) Bruce
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