Date: Fri, 6 Sep 2002 11:05:18 +0200 From: Bernd Walter <ticso@cicely9.cicely.de> To: Terry Lambert <tlambert2@mindspring.com> Cc: John Baldwin <jhb@FreeBSD.ORG>, Andrew Gallatin <gallatin@cs.duke.edu>, freebsd-alpha@FreeBSD.ORG Subject: Re: ithread preemption Message-ID: <20020906090517.GI13050@cicely9.cicely.de> In-Reply-To: <3D78098B.CEBF13EC@mindspring.com> References: <XFMail.20020905163105.jhb@FreeBSD.org> <3D78098B.CEBF13EC@mindspring.com>
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On Thu, Sep 05, 2002 at 06:48:59PM -0700, Terry Lambert wrote: > John Baldwin wrote: > > > Hey ... I think you have it on the nose! That makes the most sense > > > I've heard yet. > > > > > > Do we have any way to bind a thread to a cpu? > > > > I used to. Then KSE3 was committed. I suppose I could rewrite it from > > scratch again. > > The ithreads are different from threads. People don't seem to > get this idea, but it is nevertheless true. > > The x86 SMP doesn't have this problem (yet), in that the IRQ > is disabled on the I/O APIC, so it doesn't matter what CPU it > runs on, it's a seperate thing. Interrupts are disabled globaly on alpha too. The only platform where we disable on the CPU is the PC164 as a workaround, but this system is UP. > If x86 NUMA systems are ever supported, or in some cases the > AMD Alpha-derived arbitration is used, there could be a problem > (but not for the same reasons as on the Alpha). I expect ithreads to be one of the less critical points on NUMA. > Using all the same primitives for ithreads as for threads will > lead to things like a shared IRQ which comes true for multiple > devices will need to count down to enable, if the ithreads for > servicing are run simultaneously on seperate CPUs. This also > implies a global lock on enabling a newly arrived device that's > sharing an already allocated IRQ, and inter-CPU contnetion on > any IRQ whose use cont is != 1. Currently shared interrupts also share an ithread. > Interrupt threads make some very messy thing elegant, but they > do so at the cost of moving the mess elsewhere. If you have to > characterize it, call it "The law of conservation of inelegance". > 8-). The only thing that ever saves you from it is a top-down > design. Possible, at least that's our current design. -- B.Walter COSMO-Project http://www.cosmo-project.de ticso@cicely.de Usergroup info@cosmo-project.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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