Date: Thu, 13 Jan 2005 22:05:22 +0100 From: Anthony Atkielski <atkielski.anthony@wanadoo.fr> To: freebsd-questions@freebsd.org Subject: Re: Hyperthreading hurts 5.3? Message-ID: <1345467628.20050113220522@wanadoo.fr> In-Reply-To: <41E6DC30.3040501@netfence.it> References: <200501121049.j0CAnJQe028309@mp.cs.niu.edu> <828997113.20050112184556@wanadoo.fr> <41E58E53.7060606@netfence.it> <786252184.20050113014354@wanadoo.fr> <41E65688.4010700@netfence.it> <1242214203.20050113205210@wanadoo.fr> <41E6DC30.3040501@netfence.it>
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Andrea Venturoli writes: AV> I've come to the same conclusion. Still I can't put this together with AV> 100% load on both processors. If, as someone said, there is only one AV> FPU, *how* are these figures coming out??? The operating system tracks a dispatch of a processor into a process thread. After that, it has no idea whether the processor is actually doing anything or not--from the OS' standpoint, the processor is "running." So if one thread in one logical processor is actually executing instructions, and the other is stalled while waiting for a shared resource in the processor, the OS will still consider both threads to be "running" and will charge all of the elapsed time as processor time ... giving you a figure of 100% busy. AV> I would have expected something like 50%-50% (instead of 100%-0% of AV> the single threaded version). *If* there is only one FPU, I'd expect AV> both virtual processors being frequently idle waiting for each AV> other. Yes ... but the OS can't see that, and so OS monitoring tools can't report it. -- Anthony
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