Date: Wed, 1 May 2002 16:22:14 -0400 (EDT) From: Andrew Gallatin <gallatin@cs.duke.edu> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-smp@FreeBSD.org Subject: RE: hlt when idle? Message-ID: <15568.20086.979721.992191@grasshopper.cs.duke.edu> In-Reply-To: <XFMail.20020501161528.jhb@FreeBSD.org> References: <15567.62317.677224.3470@grasshopper.cs.duke.edu> <XFMail.20020501161528.jhb@FreeBSD.org>
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John Baldwin writes: > > On 01-May-2002 Andrew Gallatin wrote: > > > > > > Can somebody remind me why we do not hlt in the idle loop on MP x86s? > > Is this because a HLTed CPU is not going to notice a new runnable job > > (possibly migrating from another CPU) until it gets an interrupt to > > wake it up? > > Yes. This seems to be an acceptable "loss" in performance in environments where cooling is a concern. Is there a deadlock danger? Or is it just a performance tweak to not HLT SMPs? Would you object to making it a sysctl (machdep.smp_idle_hlt)? > > Do both CPUs get clock interrupts on x86? > > No, the interrupts seem to be round-robin, but each clock intr is only > sent to one CPU unlike on alpha where they are broadcast. So each CPU gets (1/num_cpu) * hz clock interrupts/sec? Drew To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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