Chapter 1: What is the main topic discussed in this episode?
You can hear me, I hope. Yes, you sound great, Brian. Oh, thank you. I'm like, why am I asking this? Because this would have been... Adam now has 25 minutes to coordinate a prank that I have lived in fear of, which is he will connect and we will act like we can't hear him. Okay. Here's what I'm going to say. First of all, that would be hilarious.
Second, I think since the pandemic, that has felt too mean. It's cool. I agree. It's cool. Because I feel like there is nothing more that cuts deeper in your soul than the like, we can't hear you. It's like when my family tells me the Wi-Fi is out, it's like I have failed as a father and provider. I have one job.
That's funny because my family doesn't like to leave that last bit as an implication. It usually is the Wi-Fi is out, you have failed as a father and provider as kind of one sentence. It's delivered as a short object. Or what my now 18-year-old but forever 13-year-old mischief maker in my mind says,
You know, the thing he used to do is any new anything that we would get, he would seize onto the parental controls before we did and then lock us out of it. Smart. You heard me as well. Yes. Yeah. Got Jordan here. I'm in the letterbox. Yes. Hey, let's do a quick roll call just to make sure we don't do like mid-show bullshit, although that's fun. Nathaniel, can we hear you? I hope so.
Yeah, that's right. How about... It's like a Mouseketeers thing? Yes, exactly. Eric? Yes. And Alan? Yep. Cliff? I'm not actually here. And finally, RFK. I'm here. Wonderful. Okay. I just wanted to make sure we had... You're not calling Alan? I did call on Alan, didn't I? Oh, you know what? Okay. Yes. Sorry, Alan. All right. Sorry. I'm doing the thing that you told me I do, Alan. I'm so sorry.
Alan, you remember me, right? I work for you? Is Alan muted for everybody else? He's really quiet. Oh, and Jordan. Jordan's here. Jordan's here. Why don't you kick us off in a less Mouseketeers fashion? Mouseketeers, okay, and I know Jordan, and Jordan, I'm sorry, just to accept the fact that we're just going to be doing this for our entire lives.
Jordan is like my generational check for millennials of like, do millennials know this? Ask Jordan. It's a lot of pressure. It is a lot, but you deliver under pressure, and that's why I call you. Mouseketeers, is that a reference that you... Uh, I know. Yeah, that's interesting. Cause what about Oregon trail? Oh, what's that Eric? Oregon trail. Oregon trail. I do know. Oregon Trail, yes.
Mouseketeers, no. I mean, it kind of makes sense because Mouseketeers was old when we watched it. True, but the Zoomers now, like my son has watched Mouseketeers, like a new kind of Mouseketeers. I know, there's going to be, I mean, there's a bit of a generational pincer move here where Xers and Zoomers both know something that millennials don't.
And it was, I mean, sorry, Jordan, to do this again to you, it was super satisfying when I had lingo from the kids and Jordan's like, What is that? Like, what do you mean? What is Loki? Like, what do you, why? I'm like, okay, I'm not going to explain it to you. It turns out that I age too. Yeah, exactly. It turns out. See, you are a great spokesperson for your generation. That's perfect.
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Chapter 2: How did the Oxide team identify the source of hardware failures?
So like our U.2s are hot plug capable. So you'll see that when you yank. But like you're supposed to tell the OS that you just did a surprise hot plug or unplug. And, you know, there are things. And so then it knows to like go re-init the thing when it comes back.
So there are some cases, but at least in our system, and I think especially at that time, I'm not even sure we had all of the hot plug machinery in place. We're really not expecting to lose all 10 of the disk drives. at any one point in time. Yeah, and I think, Nathaniel, this gets us to actually a really important juncture.
And we've described this kind of juncture before, but we've had a couple of these in the company where we haven't seen this very frequently. We don't know how to reproduce it. It's not reproducible at all for us. We have some information, but we would like to have a lot more information. And I think it's really important to not throw up your hands at that point
but rather to ask ourselves kind of collectively the question, what information do we wish we had? And then what do we need to go do to modify the system to gather that information? I mean, I kind of call this a half measure, but honestly, that information, that data can be very valuable anyway. And we had a bunch of ideas for things that we wanted to go do
And I think that Keith had talked about PCIe hot plug event counters, for example. Um, and cause what you ideally want are things that can really disconfirm a hypothesis where if, you know, if the PCI hot plug event counters are correct and are zero, then, you know, like that, and you see this again, you're like, okay, that's not it. Um, that we, um, we wanted to go add some missing reports.
Um, we did want to go follow up on the firmware side of it to figure out what was going on there. Maybe we had a firmware update, go check that, those bugs. We wanted to get some ā we did wonder if there would be other witnesses to the crime of the ā I mean, at this time, I would say I felt that, like, this is a ā this feels like a ā
That somehow we are doing something incorrect because what we're doing is so gutsy with respect to the microprocessor and that we don't have a GISA, we don't have UEFI firmware, and we've talked about this ad nauseum, that we don't have a bias and we do our own low-level platform initialization. But you're always thinking like any platform problem you've got, like you're responsible for.
And my personal thinking, and Nathaniel, I'll be interested in others what your kind of thought was, but like this is a stray purse coming to every drive because something in the AMD firmware is confused because we haven't done something correctly. It's kind of what, I don't know. Do you think that was kind of like the collective sense of where this thing likely was? It feels like that way anyway.
I mean, I think that was certainly possibly on the scene. I mean, when I'm looking at the issue, I mean, we started probing shark fins. So we have a little board that's kind of a right angle up off the main board that plugs into a SEM connector, and then the U.2s all connect to that. And that board has a little bit of circuitry there, and it manages the, like, PERS and everything.
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Chapter 3: What challenges did the team face during their investigation?
There was nothing in the IBC that indicated it had any fault. The IBC is like, I don't know, why is everyone looking at me? Yeah, in hindsight, we need to actually probably figure out why that is because that seems wrong, but you're right. So this DC-DC converter has an internal black box memory by analogy to the black box on a plane that they use to record crash data.
And it's always recording a bunch of signals in like a circular buffer. And when certain events happen, it captures it and we can pull it out. So we go to it and we get this black box data and it says, yeah, here's my black box and everything's fine. What are you talking about? Why are you talking to me?
And I also think, I mean, before we, before we like, we also have a hot swap controller in front of the IBC. And, and so like, there's a whole nother like power switch out there with a bunch of stuff. And we, we also have ignition control of the IBC. Right. So like if, if the IBC is turning off, I think our first inclination is maybe our circuits upstream are doing that. Right. Right, right.
And what did we ā I think we had already ā fortunately, we could instrument that as well. And I think we determined that this is ā we're not actually seeing a dip on the bus bar. Right, right. And RFK did ā I mean ā a bunch of surgery on these things because none of this stuff is super easy to measure or instrument in the rack.
Because our neat blind mate sleds that don't have any cables out the front mean that we don't really have any cables out the front. And it's tough to get scope probes and stuff in there. So RK did a bunch of work there. Yeah. And I think a bunch of work moving stuff around, too. Like, it was like, oh, we didn't learn anything when this happened. RFK, can you move some probes around? Yeah.
Well, what was kind of cool about the whole thing is we had just purchased these brand new scopes which had, like,
10 inputs and that was cool because it's really eight but so that way i'd be like well you know if we're gonna have to move this around at least we can sample a lot of things every time i go back to take all this crap apart because it takes forever to do it good uh i mean just to the point of not having any cables you remove all the drives um run all these long wires out there roll and plug it into the rack roll the scope over to the front of the rat kind of like
organize all this crap in some reasonable way, let it run for three days. And eventually you get something happen and then go back, pull it out, unhook or unsolder all these different from all these different points and decide which ones you want to keep. And then where you solder a whole bunch of them and run it all over again. It took a long time.
And were you, I mean, I was definitely worried that we would have a literal probe effect here that we would. Sure. Yeah. Yeah. Yeah, I mean, it got to the point where we, we're not going to say what we found yet, but we were running out of things to look for. And so we got the near field probe out, which is like when you've gotten to that point, you're like, oh, you're not going to find shit.
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Chapter 4: How did the team utilize crash dumps for debugging?
As you say, we're measuring power in, power out. And I dropped your analysis, the PDF of your analysis into chat so people can kind of see. I think this is important. The part is a... It's a Flex part. Flex bought... Actually, the IBC originates at Ericsson, which you still see artifacts of acquisitions in the product IDs that these things have.
So this thing has a four-character product or manufacturer name that comes through as Eric, E-R-I-C. And I'm like... Damn, some dude named Eric decided to like make himself and they're like, Oh, no, wait a minute. No, I think this is Erickson is what they're this is not, I guess it is some dude named Eric, but he's an entire company, not an actual Um, the title legacy anyway.
Um, but we, um, so this is the flex BMR four 91 is the part. And our kid, you want to describe kind of like collecting all of this data in the document, because it was very important to us to kind of go to flex with like, here is the, the, the totality of our investigation. We don't want to, you don't want to drop this on your lap by any means, but we need your help.
We took select shots of kind of like the damning, uh, problem uh we found this droop and how long is it you should describe the actual length of the truth i mean it's only like you know 12 milliseconds about you could kind of and um really what was interesting about the droop is that you can tell from the from the waveform it's it's a controlled ramp
Which is different than you would see in something like a discharge or just because the controller is doing this purposefully for some reason and it's in such a fine time frame that it's like, you know, it exceeds the, you know, restart time frame for the part. So that kind of like is weird. It's really hard for us to induce this by, you know,
maybe we have noise on the the reset pin or like something like that with something weird and we we've also scoped all those things too and the answer is no we don't do that um maybe maybe ignition's got some odd noise that like i we we really kind of poked all around and we i've kind of labeled out uh on all these different inputs what what we were looking at and um it kind of really put it together where it's like look this
Something is up with the IBC, not us. Yeah. Your logs don't even really make a whole lot of sense. So we really need your help because I think it's you. Right. This is like three milliseconds down, four milliseconds-ish. up. So, and you, I mean, this is the kind of the amazing thing about like this troop is like not very long.
I mean, this thing is, I mean, you know, this is, you know, I, you know, I, I, I had, I had one of my three children who will remain unnamed did very poorly on a math test. And in talking to that individual about their performance of the math test, they pointed out that they got half of them, right. And I'm like, well, that is true. You did get half of them, right? Yeah. Yeah. Total optimist.
You did get half of them, right. Um, but the problem is the other half. And I feel like the IBC would be like, Hey, I've been, I mean, I am, I've been doing this all the time. I am at, I'm holding this 12 volt rail. And yeah, like I took a quick, I took a quick break. Yes. I stepped out for six milliseconds and, How many nines of uptime does this rail have?
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Chapter 5: What role did the IBC play in the hardware issues?
And incidentally, the mitigation was provided to us as a sequence of undocumented hexadecimal numbers we were supposed to poke into registers, because of course it was.
So I had to reverse engineer it, and we eventually worked out what it was doing, which was because of the component choices on the analog front end, the part, the IBC, was particularly sensitive to deciding that there was a voltage droop on the input when there wasn't really. And it has a very nice designed-in feature to cut power if the voltage droops out of range.
In fact, it's a programmable feature, which is great because what the mitigation was doing, it turns out, was programming that to stop doing that or concretely to turn off the entire undervoltage detector. That's generally a bad idea because you were using that under-voltage detector for something.
But in our case, it's actually probably fine because the mitigation turns off that, but then turns on some other features that kind of paper over it and mostly ignore it. But more importantly, we had our own upstream under-voltage detector in the hardware that we had installed in advance of the IBC. It's one of these hot plug controllers we mentioned.
What we wound up doing is working all of their numbers backwards, finding a couple of unit conversion errors, because math is hard. I mean, I do unit conversion errors all the time. And then figuring out what the right numbers should be and plugging them into the IBC, and then the problem appeared to go away. And then that RFD describes the actual math, but it's probably not very exciting.
And so the great thing about that is like, this is something that we can now do in the field, which is great. We can now, hey, that bone pile, we can now like, we can, okay, this doesn't, this sounds worse than it is. We can ship the bone pile now. We can actually like... Well, or at least we can, we can recharacterize the bone pile, right?
We can take those machines, we can feed them back through and figure out how many of them seem like they work now and how many of them, uh, turns out have some other problem that this was masking. Totally, totally. And we, which is great. Um, and then we are, um, and then importantly we can, uh, and Jordan, this is where, you know, you, you were,
making progress in your work, be like, actually, if this is not going to be an issue, we've got, it's not like there are not other, there's nothing else to do. Yeah, exactly. You're just like, I've got like 8 million other like super hot priorities. So I'm happy to kind of put this one on the back burner. If we can work, work around it.
I thought one of the things that I thought was really interesting. And I don't mean Nathaniel, Eric, RFK, maybe I shouldn't be surprised by it, but once the Cosmo population got large enough to, We started seeing it at basically the exact same rate we saw in Gen 1.
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