Date: Tue, 1 Feb 2005 23:34:04 +0100 From: Bernd Walter <ticso@cicely12.cicely.de> To: John Baldwin <jhb@FreeBSD.org> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/alpha/alpha machdep.c src/sys/alpha/include cpuconf.h src/sys/alpha/pci lca.c lcareg.h Message-ID: <20050201223403.GE31822@cicely12.cicely.de> In-Reply-To: <200502011132.13288.jhb@FreeBSD.org> References: <200501312307.j0VN7gxm080740@repoman.freebsd.org> <200502010649.33768.jhb@FreeBSD.org> <20050201152803.GC31822@cicely12.cicely.de> <200502011132.13288.jhb@FreeBSD.org>
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On Tue, Feb 01, 2005 at 11:32:13AM -0500, John Baldwin wrote: > On Tuesday 01 February 2005 10:28 am, Bernd Walter wrote: > > Would the PAL call work for SMP systems? > > Yes, though it says that the CPU counter can slow down while it is in the > waiting state, so it seems that PAL is free to implement something just like > what you did. I'm more worried about wakeup e.g. in case of one CPU releasing a lock another is waiting for. > > AFAIK no alpha CPU has native halt support so there is not much magic > > that PAL can do for us. > > What I've found out about this case is that alpha CPUs automaticaly > > reduce power on unused parts and running just a tight loop, that works > > without memory access, for a few microsecsonds might be more efficient > > do do it ourself than calling PAL, which must be doing something > > similar. > > At least I think it is possible to reduce idle power consumption from > > the current situation either way. > > Yes, right now we buzz loop with a memory access on each iteration, we could > add a for loop that just decrements a counter to zero to the idle loop if > desired. With preemption turned on we could have the idle process not check > the run queues at all and just sit in a buzz loop. Exactly this is what I was thinking about, but wanted to do power measurements first. But my priority has more interessting stuff first - the lca code already existed for years now. -- B.Walter BWCT http://www.bwct.de bernd@bwct.de info@bwct.de
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