[1]: https://undo.io/resources/undo-performance-benchmarks/ - "Undo serializes their execution"
Undo has cool features like Live Recording that we don't have in rr. They don't need access to the hardware PMU which is a big advantage in some situations. They can handle accesses to shared memory in cases where rr can't. https://undo.io/resources/undo-vs-rr/ is a good resource.
It may not be commercial quality but its open source and free :)
[I built rr.soft]
Technically:
* Doesn't need hardware performance counters - runs on more CPUs and on cloud systems (where performance counters are often blocked).
* Can attach and detach at any time - means you get to record just a subset of program execution that's interesting.
* You can our ship recording tech with your application and control it by API, so you can grab crash recordings on customer systems.
* Supports programs that share memory with non-recorded processes.
* Supports direct device access (e.g. DPDK).
* Accelerated debugging features - searching with recordings using parallel processing, accelerated conditional breakpoints a few thousand times faster than native GDB.
* We provide a stable, patched fork of GDB that we're occasionally told is more stable than the default.
For many people's use cases none of these really matter - they should use RR if they're not already.
But if you need any of these things then Undo can give you time travel debugging. In practice, it's usually big software organisations that we deal with because they have development pain and the extreme requirements we can match.
That’s actually pretty neat.
Before it was released publicly I believe Microsoft had been using it internally to share recordings on bug reports against massive pieces of software like Office. So it's a serious piece of tech.
https://sourceware.org/gdb/current/onlinedocs/gdb.html/Proce...
But it's limited. It's really cool that it's integrated by default but it doesn't scale to big applications / workloads.
RR and Undo both use GDB as a user interface, though, so any skills you have there will carry over.
All these Oh wait. I missed it...debugging sessions. and these What exactly changed over there? are answerable.
I've thought I bit about how you might support time travel on bare metal embedded - but actually there are hardware-assisted solutions (Lauterbach's Trace32 was one we came across) there sometimes.
The category namer of time-travel debugging, TimeMachine, (hence time-travel debugging in contrast to other attempted names such as reversible, bidirectional, record-replay, etc.) was available in 2003 and supports/supported the ARM7 [2]. Note, that is not ARMv7 architecture, that is the ARM7 chip [3] in use from 1993-2001.
From what I know, the ARM7 was one of the first ARM designs implementing the Embedded Trace Macrocell (ETM) which could output the instruction and data trace data used to support trace probe-based time travel debugging.
[1] https://jakob.engbloms.se/archives/1564
schaefer•8mo ago
Pricing & Licensing
A UDB floating license costs $7,900 per year.
dima55•8mo ago
Veserv•8mo ago
This, of course, ignores employee benefits and overhead which usually amount to ~100% extra costs over direct pay. So that is now ~1.1% and ~2.1%, respectively.
And that ignores the fact that you need to pay people less than they produce to be profitable which probably drops us down to ~0.5% and ~1.0%, respectively.
[1] https://www.levels.fyi/companies/google/salaries/software-en...
edit: Incorrectly linked to product designer instead of software engineer levels.
dima55•8mo ago
esafak•8mo ago
Veserv•8mo ago
If your employer really is skeptical, then they can run a A/B test over a small group of engineers to prove out changes in productivity. But not even being willing to run that test when it is so cheap is just management incompetence.
Engineers are ridiculously expensive. In electrical engineering, where the engineers are generally less well-paid than in software, employers routinely spend multiple hundreds of thousands of dollars per engineer per year in tooling. Not being willing to spend 8 k$ on a test of well known technology and attempting to identify mere single digit percentage improvements is just stupid.
ranger_danger•8mo ago
Please try to understand that the world is not as simple and black and white as you'd like.
more-nitor•8mo ago
if someone's bringing "google payscale" for comparison... well that's not some average joe...
why not just bring Bill Gates and say "everything -- including private jet -- is dirt cheap" ?
$8k per year simply doesn't make sense for 95% of the programmers. For a lot of developing countries, that's more than a well-paying programmer's annual salary...
Veserv•8mo ago
IF you are such a company, THEN you only need very minor productivity improvements to justify such a price difference. IF you are such a company, THEN such costs are well within the cost of doing business. IF you are NOT then you are free to apply your own numbers to your situation.
However, the overwhelming majority of companies that fall into the applicable category outright refuse to even consider the possibility of a 8 k$ capital expense on software development tooling out of the absolutely foolish belief that such expenditure CAN NOT be justified as such a cost could not possibly be recouped in benefits or out of the absolutely foolish belief that a product that costs 100$ must be 100x better than a product that costs 1$ to be justified, and thus a product that costs money must be infinitely better than a product that is free to be justified.
It is absolutely management incompetence for US employers to just shut down upon hearing about a 8 k$ capital expenditure instead of doing a proper cost-benefit analysis to determine if such expenditures would be justified.
db48x•8mo ago
That said, if you’re going to spend money on a debugger then I recommend rr + Pernosco instead. Pernosco is a completely different kind of debugger that will make you much, much more productive at debugging than any traditional debugger where you start by adding breakpoints and then stepping through your code. Costs a lot less too.
Veserv•8mo ago
Very well, a software engineering employer in the US who employs over 10 software engineers in the US at above the 20th percentile of wages, which constitutes the employers of a significant fraction of total software engineers above the 20th percentile of wages, would be foolish to not spend 8 K$ on software development tooling that would result in a 10% productivity improvement. It would be further foolish to not investigate such potential improvements given a reasonably credible belief that such a productivity improvement is possible. Outright dismissal without even considering the potential cost-benefit or making a incorrect cost-benefit analysis requiring significantly in excess of 10% is also foolish.
Please try to understand that sometimes when people are not being utterly pedantic to the point of absurdity it is because they assume people will use their judgement to interpret the applicability to their situation rather than because they can only see in black and white.
db48x•8mo ago
gregthelaw•8mo ago
Why do people pay for Undo when they can get rr -- which is also really good -- for free? Those whose code or environment is big enough and complex enough that rr doesn't work for them, and they understand how powerful time travel debugging is. If rr works for you, you should use it. This includes most independent developers.
If rr can work for you and you're still not using any kind of time travel debugging, you have effective tied one hand behind your own back! If you're independent (incl student or academic) and rr doesn't work for you, get in touch -- we give free licenses for academic and certain other use cases.
There is a wider thing here about software companies paying for dev tooling. So many companies over the years who made really cool things who couldn't make their business work.
db48x•8mo ago
Completely agree about that! I’ve used rr to debug things that I never could have without it. People are resistant to change though.
eviks•8mo ago
AlotOfReading•8mo ago
I was in talks with them recently because I kept running into limitations with rr. The main advantages for my use case were that undo doesn't have the same dependency on hardware timers, which means the ARM support is much better, you can run it in a VM (e.g. a cloud machine) and you can do replays on different systems.
dzaima•8mo ago
- If your program is very light on syscalls (i.e. basically entirely in-memory computation), rr can go to a basically 1.0x slowdown. In particular this means you can run benchmarks in it at full capacity, provided that I/O is outside of the repeated part (e.g. if sometimes the bench is noticably slower, you can replay and see if some important loads/stores crossed a cacheline/page). You can even "perf record" / "perf stat" a replay if you want to! (none of this is too useful, but it's fun! Gathering repeated stats over the same execution for more resolution might be useful with proper tooling though)
- rr does have an in-memory buffer of recording data.
- rr recordings should be portable within the architecture, as long as the replay hardware has the extensions the recorder did (or if replayer-unsupported features are disabled at record-time).
AlotOfReading•8mo ago
gregthelaw•8mo ago
Undo is mostly used by companies whose world is complex enough that rr doesn't work for them, and they understand how powerful time travel debugging is.
There has now been a LOT of engineering invested by a lot of very smart people into Undo, so it does also have a lot of polish and nice features.
But honestly, if rr is working for you, that's great. I'm just glad you're not doing printf debugging the whole time :)
db48x•8mo ago
rurban•8mo ago
db48x•8mo ago