Gabriele SveltoA few years ago I designed a way to detect bit-flips in Firefox crash reports and last year we deployed an actual memory tester that runs on user machines after the browser crashes. Today I was looking at the data that comes out of these tests and now I'm 100% positive that the heuristic is sound and a lot of the crashes we see are from users with bad memory or similarly flaky hardware. Here's a few numbers to give you an idea of how large the problem is. 🧵 1/5
In the last week we received ~470000 crash reports, these do not represent all crashes because it's an opt-in system, the real number of crashes will be several times larger. Still, out of these ~25000 crashes have been detected as having a potential bit-flip. That's one crash every twenty potentially caused by bad/flaky memory, it's huge! And because it's a conservative heuristic we're underestimating the real number, it's probably going to be at least twice as much. 2/5
In other words up to 10% of all the crashes Firefox users see are not software bugs, they're caused by hardware defects! If I subtract crashes that are caused by resource exhaustion (such as out-of-memory crashes) this number goes up to around 15%. This is a bit skewed because users with flaky hardware will crash more often than users with functioning machines, but even then this dwarfs all the previous estimates I saw regarding this problem. 3/5
And to reinforce this estimate I've looked at the numbers we got from the users who run the memory tester after having experienced a crash: for every two crashes we think are caused by a bit-flip the memory tester found one genuine hardware issue. Keep in mind that this is not doing an extensive test of all the machine's RAM, it only checks up to 1 GiB of memory and runs for no longer than 3 seconds... and it has found lots of real issues! 4/5
And for the record I'm looking at this mostly on computers and phones, but this affects *every* device. Routers, printers, etc... you name it. That fancy ARM-based MacBook with RAM soldered on the CPU package? We've got plenty of crashes from those, good luck replacing that RAM without super-specialized equipment and an extraordinarily talented technician doing the job. 5/5
Steven Op de beeck@gabrielesvelto My mind was going to cheap low-end hardware, but now you’re throwing expensive Apple Silicon SOC’s in the mix, it’s a bit harder to believe that they suffer from bitflips at the rates your are implying.
@stevenodb high-end hardware pushes the limits of semiconductors both because of small feature size and high clocks increasing the chances of failure. In the case of DRAM the chance of malfunction increases with higher temperature too, as the ability of trench/stacked capacitors to retain charge degrades with it... and Apple puts its DRAM right next to the CPU, the single hottest place of the whole device.