Let's put aside for a moment the latency we marked orange to compare the read bandwidths between 7900X and 6900K.
In terms of bandwidth, on the L1, one is in practice slower by 11% in reading and a little bit more in writing. Nothing serious, if we compare to Ryzen for example, Intel continues to have L1 excessively fast.
On the other hand when looking at the L2, things are all different. Of course, the write / copy bandwidth is only 12/13% lower, but the read bandwidth is divided by three! We have not given it back on this chart, but this figure of read bandwidth is even less than ... Piledriver. One will remain cautious, as we will see a little below the L2 seems to have a different operation than what the raw features provided by Intel can suggest, and this probably impacts this bandwidth value.
But if we now look at the L3, things are in the same line. This time the reading / copying operations are twice slower on Skylake-X than on Broadwell-E, and in reading, performance is divided once again by three.
In other words, these figures are not good, and if once again we will remind you that it is possible that Aida64's measurement tools do not correctly detect certain details, or are not adapted to certain features of Skylake- X, the general order of magnitude seems to be this.
As far as latency is concerned, here too we are cautious. The latency of the L1 is similar, but that of the L2 increases, lining up a little more on Zen than on Broadwell-E. And for L3, again, the latency is very high, almost 50% higher than that of Broadwell-E.