Date: Tue, 01 Jan 2008 10:49:34 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: rrs@cisco.com Cc: cvs-all@FreeBSD.org, cvs-src@FreeBSD.org, src-committers@FreeBSD.org, jhb@FreeBSD.org, brde@optusnet.com.au Subject: Re: cvs commit: src/sys/netinet sctp_bsd_addr.c Message-ID: <20080101.104934.1346822828.imp@bsdimp.com> In-Reply-To: <477A2D6D.9030403@cisco.com> References: <20080101161858.A10345@delplex.bde.org> <20080101.024546.1079618522.imp@bsdimp.com> <477A2D6D.9030403@cisco.com>
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In message: <477A2D6D.9030403@cisco.com> Randall Stewart <rrs@cisco.com> writes: : M. Warner Losh wrote: : > In message: <20080101161858.A10345@delplex.bde.org> : > Bruce Evans <brde@optusnet.com.au> writes: : > : 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. : > : > Do we want to document the other Pxxxx priorities? : > : > : 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.) : > : > So would the following be a reasonable change to sleep.9? : > : > Index: sleep.9 : > =================================================================== : > RCS file: /home/ncvs/src/share/man/man9/sleep.9,v : > retrieving revision 1.61 : > diff -u -r1.61 sleep.9 : > --- sleep.9 30 Mar 2007 18:07:26 -0000 1.61 : > +++ sleep.9 1 Jan 2008 09:44:01 -0000 : > @@ -93,6 +93,10 @@ : > runnable with the specified : > .Fa priority : > when it resumes. : > +.Dv PZERO : > +should never be used, as it is for compatibility only. : > +A new priority of 0 means to use the thread's current priority when : > +it is made runnable again. : > If : > .Fa priority : > includes the : > : > Warner : > : That sure would have been nice to read in the manual page .. I would : have not changed this at all if I would have had that to read :-( : : I was pinged on xchat over an issue where the sctp worker thread : was hanging... and in the process I was told that 0 was max : priority.. which really concerned me... 0 having a special : meaning of.. "don't change my priority" means the old code : was fine :-0 : : Not that having a mid-range lower priority is a bad thing : for this task... I had someone point out that I wasn't using PZERO in the code I wrote at work, so I went through and changed all the drivers there to use PZERO always. The fact it is compatibility shimming wasn't clear at all, hence my desire to document it :0 Warner
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