From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Date: Mon, 10 Nov 2008 15:22:53 +0000 Subject: Re: [patch] remove vcpu_info array v5 Message-Id: <491851CD.9030401@us.ibm.com> List-Id: References: <4909C00F.8050704@sgi.com> In-Reply-To: <4909C00F.8050704@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kvm-ia64@vger.kernel.org Avi Kivity wrote: > >> My patch gets rid of the pointless MAX_CPUS sized array, which doesn't >> buy us anything. In fact, most of the changes in my patch makes the >> code simpler, because it removes a stack of silly cases where qemu uses >> env->cpu_index to get into the array, just to hide CPUState from libkvm, >> just to have the callback in QEMU go from int vcpu back to CPUState. >> >> Lets just do it right and get rid of this silliness. > > I agree that vcpu_info should die. But we should still have a fast > way of getting a cpu from a cpu_index. I don't see a problem with a > static array of pointers, make it 16K in size if you want. Our real > scaling limits are much lower; they involve the big qemu lock and the > single iothread which will both limit scaling far below any static > vcpu array. Just do a linear search of the CPUState list and be done with it. This smells of premature optimization greatly. I would be amazed if walking the CPUState list is ever on the fast path or will ever be. Really, if you need to go from cpu_index => CPUState, it suggests you're doing something wrong. Regards, Anthony Liguori