Exclusive Q&A with Atom architect Jon Tyler regarding Silvermont:
1. Could you please help me understand the competitive positioning of Silvermont to A15 and, perhaps, A57? Intel claimed that Silvermont IPC will be about on-par with A15, despite having a narrower front end/back end, smaller OoO structures, lack of FMAC capability, etc. So, my real question is: what gives you confidence that Silvermont stays this competitive with A15 on integer workloads (this is what the competitive comparison at the uArch disclosure talked about) despite the narrower design? Further, should we expect that Silvermont is as competitive on floating point with the ARM design as it is on integer (this is what was highlighted at the talk)?
We have A15 measurements, and Silvermont measurements, so confidence here is based on actual measurements we’ve seen. (We cross-check these results with what ARM quotes themselves)
We’ve done a lot of analysis and there are many areas where we have an advantage: our memory latency (at each level of cache hierarchy) and memory BW, our superior branch handling, our complex-instruction support, our smart resources management, and many other things, allow us to outperform.
From Silverthorne to Silvermont, gains on FP workload should be even better than gains on integer workloads.
Again, we have A15 measurements, and Silvermont measurements, and are confident in our FP scores are similarly impressive.
2. Silvermont products hit the shelves in late 2013, which implies that the competition may not be the A15 for too long and instead will be the A57 (and updated micro-architectures from Qualcomm, Apple, etc.). Do you guys believe that Silvermont, built on the 22nm process, stays competitive against these new parts on performance and performance/watt, or do we need Airmont to get that lead back? I guess broadly, my question is, do you see Intel maintaining a continuous lead from here on out, or should we expect "leap-frogging" until the Atom schedule is more in-line with the Core parts in terms of process technology?
Silvermont should continue to be very competitive against even what we project as 2014 offerings.
3. I saw very interesting comparisons of Silvermont with Saltwell in the disclosure. What puzzles me, though, is that it is very difficult to get a read on CPU-limited performance of these low power micro-architectures. For example, a benchmark like "Geekbench" paints "Saltwell" in a rather unflattering light compared to the ARM contemporaries, but then you see benchmarks such as AnTuTu showing a 2C/4T Saltwell taking leadership positions againt a 4C/4T "Krait" or even Cortex A15 in integer and memory bandwidth, while even staying competitive on floating point! Could you help me to understand how Saltwell compares to the competition from what you have seen with more sophisticated measurements, and then from there I have a lot better context to think about Silvermont performance?
Geekbench is interesting: you look at the results, and the main “unflattering” results are in a few sub-benchmarks, where the IA version is set up to handle denorms precisely, and the input dataset is configured to be 100% denorms. This is not normal FP code, not a normal setup, and possibly not even a apples-to-apples comparison to how ARM is handling these numbers. So we view this as an anomaly. (The Geekbench developer agrees with us)
Saltwell trails A15 in raw IPC, but its higher frequency and threads are able to help compensate.
Saltwell trails Krait on very basic workloads like DMIPS, but on more complicated workloads Saltwell’s robust architecture will pull ahead.
