Hacker News Reader

Comment by thegeomaster | Hacker News Reader

I get it. This frustrated me to no end. But still I did what I had to do --- recompiled random software throughout the stack, enabled random flags, etc. It was doable and now I can do it much faster. I don't think it's fair for upstream to disable a useful optimization just so I don't have to do this additional work to fix and optimize my system.

View on HN

Doing real world, whole system profiling, we've found performance was affected by completely unexpected software running on the system. Recompiling the entire distribution, or even the subset of all software installed, is not realistic for most people. Besides, I have measured the overhead of frame pointers and it's less than 1%, so there's not really any trade-off here.

Anyway, soon we'll have SFrame support in the userspace tools and the whole issue will go away.

In one of my jobs, a 1% perf regression (on a more stable/reproducible system, not PCs) was a reason for a customer raising a ticket, and we'd have to look into it. For dynamically dispatched but short functions, the overhead is easily more than 1% too. So, there is a trade-off, just not one that affects you.

If 1% shows up out of nowhere, it's very much worth investigation and trying to fix it. You shouldn't let them freely happen and pile up.

But there are some 1% costs that are worth it.

I think it comes down to numbers. What are most installed systems used for? Do more than 50% of installed systems need to be doing this profiling all the time on just all binaries such that they just need to be already built this way without having to identify them and prepare them ahead of time?

If so, then it should be the default.

If it's a close call, then there should be 2 versions of the iso and repos.

As many developers and service operators as there are, as much as everyone on this page is including both you and I, I still do not believe the profiling use case is the majority use case.

The way I am trying to judge "majority" is: Pick a binary at random from a distribution. Now imagine all running instances of that binary everywhere. How many of those instances need to be profiled? Is it really most of them?

So it's not just unsympathetic "F developers/services problems". I are one myself.

Everyone benefits from the net performance wins that come from an ecosystem where everyone can easily profile things. I have no doubt that works out to more than a 1% lifetime improvement. Same reason you log stuff on your servers. 99.9% pure overhead, never even seen by a human. Slows stuff down, even causes uptime issues sometimes from bugs or full discs. It's still worthwhile though because occasionally it makes fixes or enhancements possible that are so much larger than the cost of the observability.

This at least makes sense. Thanks.

Do 50% of users need to be able to:

* modify system services?

* run a compiler?

* add custom package repositories?

* change the default shell?

I believe the answer to all of the above is "no".

All those things are free in terms of performance though.

I don't see how this applies. Some shell has to be the default one, and all systems don't pick the same one even. Most systems don't install a compiler by default. Thank you for making my point?

All these things are possible to do, even though only developers need them. Why shouldn’t the same be true for useful profiling abilities? Because of the 1-2% penalty?

Are you serious?

Visa makes billions per year off of nothing but collecting a mere 2%-3% tax on everything else.

Visa sells money for money, skimming off a percentage.

CPUs spends cycles for features (doing useful work). Enabling frame pointers skims off a percentage of the cycles. But it's the impact on useful work that matters, not how many cycles you lose. The cycles are just a means to an end. So x% of cycles is fundamentally incomparable to x% of money.

I don't see how Visa is in any way relevant here.

I don't see why not.

The whole point of an analogy is to expose a blind spot by showing the same thing in some other context where it is recognized or percieved differently.

Reply on news.ycombinator.com