On 13/09/2012 15:25, Stan Hoeppner wrote:
On 9/12/2012 10:21 PM, GuoZhong Han wrote:This system has a 36 cores CPU, the frequency of each core is 1.2G.Obviously not an x86 CPU. 36 cores. Must be a Tilera chip.
I don't know of any other 36-core chips - but the OP would have to answer that.
GuoZhong, be aware that high core count systems are a poor match for Linux md/RAID levels 1/5/6/10. These md/RAID drivers currently utilize a single write thread, and thus can only use one CPU core at a time.
Even with multitheaded raid support, such high core-count chips are not ideal for this sort of application.
To begin to sufficiently scale these md array types across 36x 1.2GHz cores you would need something like the following configurations, all striped together or concatenated with md or LVM: 72x md/RAID1 mirror pairs 36x 4 disk RAID10 arrays 36x 4 disk RAID6 ararys 36x 3 disk RAID5 arrays Patches are currently being developed to increase the parallelism of RAID1/5/6/10 but will likely not be ready for production kernels for some time. These patches will however still not allow scaling an md/RAID driver across such a high core count. You'll still need multiple arrays to take advantage of 36 cores. Thus, this 16 drive storage appliance would have much better performance with a single/dual core CPU with a 2-3GHz clock speed.
I doubt if the OP is aiming to saturate all 36 cores. There is no need to scale across all the cores - the aim is just to spread the load amongst enough cores that processing power is not a bottleneck. If you can achieve this with four cores in use and 32 cores sitting idle, then that is just as good as running 36 cores at 10% capacity.
But I absolutely agree that it is a lot easier to achieve the required performance with a few fast cores than lots of slower cores.
The other issue to consider here is IO and memory bandwidths - high core count chips don't have the bandwidth to fully utilise the cores on storage applications.
If I were doing such a product, I'd immediately toss out the 36 core logic platform and switch to a low power single/dual core x86 chip.
I'd go for at least two, but probably four cores - the difference in price is going to be irrelevant compared to the rest of the hardware. But I agree that large numbers of cores are probably wasted.
The only reason I would want lots of cores here is if the device is more than just a storage array. For example, if you are compressing or encrypting the data, or using encryption on the network connections, then extra cores will be useful.
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