Re: [libvirt] [PATCH RFC]: Support numad

On 02/28/2012 11:34 PM, Osier Yang wrote: >On 02/29/2012 12:40 AM, Daniel P. Berrange wrote: >>On Tue, Feb 28, 2012 at 11:33:03AM -0500, Dave Allan wrote: >>>On Tue, Feb 28, 2012 at 10:10:50PM +0800, Osier Yang wrote: >>>>numad is an user-level daemon that monitors NUMA topology and >>>>processes resource consumption to facilitate good NUMA resource >>>>alignment of applications/virtual machines to improve performance >>>>and minimize cost of remote memory latencies. It provides a >>>>pre-placement advisory interface, so significant processes can >>>>be pre-bound to nodes with sufficient available resources. >>>> >>>>More details: http://fedoraproject.org/wiki/Features/numad >>>> >>>>"numad -w ncpus:memory_amount" is the advisory interface numad >>>>provides currently. >>>> >>>>This patch add the support by introducing new XML like: >>>><numatune> >>>><cpu required_cpus="4" required_memory="524288"/> >>>></numatune> >>> >>>Isn't the usual case going to be the vcpus and memory in the guest? >>>IMO we should default to passing those numbers to numad if >>>required_cpus and required_memory are not provided explicitly. >> >>Indeed, why you would want to specify anything different ? At >>first glance my reaction was just skip the XML and call numad >>internally automatically with the guest configured allocation >> > >Here the "required_cpus" stands for the physical CPUs number, >which will be used numad to choose the proper nodeset. So from >sementics point of view, it's different with <vcpus>4</vcpus>, >I can imagine two problems if we reuse the vCPUs number for >numad's use: > >1) Suppose there are 16 pCPUs, but the specified vCPUs number >is "64". I'm not sure if numad will work properly in this case, >but isn't it a bad use case? :-) > >2) Suppose there are 128 pCPUs, but the specified vCPUs number >is "2". numad will work definitely, but is that the result the >user wants to see? no good to performace. > >The basic thought is we provide the interface, and how to configure >the provided XML for good performace is on the end-user then. If >we mixed-use the two different sementics, and do things secrectly >in the codes, then I could imagine there will be performance problems. > >The "required_memory" could be omitted though, we can reuse >"<memory>524288</memory>", but I'm not sure if it's good to >always pass a "memory amount" to numad command line, it may be >not good in some case. @Bill(s), correct me if I'm not right. :-) > >Perhaps we could have a bool attribute then, such as: > ><cpu required_cpus="4" required_memory="yes|no"/> > Please keep Bill Gray on this thread. He is the author of numad and is the best person to answer the above questions.

Bill >Regards, >Osier