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I don't completely understand the perception that standard non hardened high-perf CPU, especially in an industry and more specifically in a segment that has bee
by temac 5y ago
I don't completely understand the perception that standard non hardened high-perf CPU, especially in an industry and more specifically in a segment that has been reported as consistently cutting a few corners in recent years (maybe somehow less than client CPUs, but still), should somehow be exempt of silent defaults, because... magic?
If you want extremely high reliability, for critical applications, you use other CPUs. Of course, they are slower.
So the only interesting info that remains is that the defect rate seems way too high and maybe the quality decreasing in recent years. In which case, when you are Google, you probably could and should complain (strongly) to your CPU vendors, because likely their testing is lacking and their engineering margins too low... (at least if that's really the silicon that is at fault, and not say for example the MB)
Now of course it's a little late for the existing ones, but still the sudden realization that "OMG CPU do sometimes fail, with a variety of modes, and for a variety of reasons" (including, surprise(?!), aging) seems, if not concentrating on the defect rate, naïve. And the potential risk of sometimes having high rate errors was already a very well known esp. in the presence of software changes and/or heterogenous software and/or heterogenous hardware, due to the existence of logical CPU bugs, sometimes also resulting in silent data corruption, and sometimes also with non-deterministic-like behaviors (so can as well work on a core but not another because of "random" memory controller pressure and delays, and the next time with the two cores reversed)
- ng55QPSK 5y agoI think, the main point is: We have reached a time in which there are no guarantees anymore that your HW works (until recently we only had no guarantee that the SW works). Correctly.
- antonvs 5y agoWhen was there ever a guarantee that HW worked? ECC memory was deprecated in consumer machines 15 years ago or more. This was a conscious industry choice that reliability in hardware could be sacrificed to other concerns. That's just an example.
- dataflow 5y agoPeople use ECC to protect against misbehavior that is random both spatially and temporally. That is, it's not meant to protect against the same transistors producing incorrect outputs consistently/systematically. Put another way, we felt we had a rather safe guarantee that consistent/systematic misbehavior of the same portion of hardware would be either testable (like with memory diagnostics) or nonexistent. This paper is tearing apart that assumption.
- jeffbee 5y agoWhy assume it was the manufacturer silently cutting the engineering safety margins rather that the customer asking them to do it?
- temac 5y agoBecause benchmarks sale and are easy to perform whereas characterising spurious failures is hard and unreliable CPUs are not in the interest of users of server products (and arguably not in the interest of users of other products as well but I can see gamers willing to trade stability for marginal perf improvement)