Date: Mon, 3 Mar 2008 09:25:44 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Maxim Sobolev <sobomax@FreeBSD.org> Cc: cvs-src@FreeBSD.org, Jeff Roberson <jeff@FreeBSD.org>, src-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/amd64/amd64 identcpu.c mp_machdep.c src/sys/amd64/include smp.h src/sys/i386/i386 identcpu.c mp_machdep.c src/sys/i386/include smp.h src/sys/ia64/ia64 mp_machdep.c src/sys/kern sched_ule.c subr_smp.c ... Message-ID: <20080303092335.E66705@fledge.watson.org> In-Reply-To: <47CBC127.8010403@FreeBSD.org> References: <200803020758.m227wgH9040483@repoman.freebsd.org> <47CBC127.8010403@FreeBSD.org>
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On Mon, 3 Mar 2008, Maxim Sobolev wrote: > Cool! I am just curious if the new topology code is flexible enough to > support cores that come and go on the fly? This could be useful in several > scenarios, such as for example when running under multi-core aware > hypervisor (e.g. Niagara), in the cases when pro-active power manager shuts > down some cores to conserve power, in server applications when one of CPUs > either has fried or has been unplugged, etc. We have quite a bit of kernel code that expects CPUs never come and go; I've been hoping to interest people in having a devsummit session on CPU hotplugging for a couple of years now. :-) I don't see physical hotplugging as all that motivating currently, by hypervisor reallocation of CPUs *is* immediately motivating. You'll find assumptions of fixed CPUs all over our kernel -- schedulers, memory allocators, timer management, etc. A mature model for starting and stopping CPUs and allowing kernel subsystems to register with event handlers in order to start/stop their own services is necessary. Similarly, providing a way for user applications that care about CPU placement to hook into the event stream and respond appropriately is important. Robert N M Watson Computer Laboratory University of Cambridge
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