dylanmc

dylanmc

Rust Brain Teasers: "Stacking Boxes" heap vs. stack performance explanation

Title: Rust Brain Teasers, page 47

“Because of the extra steps required for heap read/write access—particularly with frequent allocations—accessing data on the heap can be a lot slower than accessing data on the stack. Why? Because the CPU’s memory cache will try its best to keep your heap data available.”

This explanation doesn’t really make sense - both heap and stack are cached, and in both cases “the memory cache will try its best”. I think this might be trying to say something about stack memory has better locality, so the cache has an easier job, but even so, the above paragraph struck me as misleading and/or confusing.

Marked As Solved

herbert

herbert

Author of Hands-on Rust

Thank you! I’m inclined to agree, I’ll see if I can make that explanation a bit clearer for the next beta.

There’s really two things at play with stack vs. heap cache. One is locality: your stack is almost always in one of the cache levels because your program uses it constantly. The stack being tiny also helps with this: it’s easy to fit into the cache, so there’s an even higher probability that it will be there (and if it isn’t, it’s a fast operation to load a tiny stack frame into cache vs. an arbitrarily sized heap object).

Good catch - thank you. :slight_smile:

Also Liked

dylanmc

dylanmc

Yay - glad to help! While I’m here, I think the previous paragraph is also confusing:

“Reading data from the heap also requires a little more work: to read data, your program first needs to read the pointer to determine where the heap data is stored. Once it knows the location, the program can read the data from there.”

It’s confusing (to me) - accessing the stack is also via a pointer, and usually accessing the stack involves computing an offset from the stack pointer first, so…it’s not cut-and-dried easier.

One aspect of the difference between them that your discussion doesn’t yet capture is that allocating from the stack is super-cheap (moving the SP), where it’s almost rocket science what goes on in modern heap allocators.

I’m really enjoying the book so far - I’ve learned a lot already!

Where Next?

Popular Pragmatic Bookshelf topics Top

jimmykiang
This test is broken right out of the box… — FAIL: TestAgent (7.82s) agent_test.go:77: Error Trace: agent_test.go:77 agent_test.go:...
New
raul
Hi Travis! Thank you for the cool book! :slight_smile: I made a list of issues and thought I could post them chapter by chapter. I’m rev...
New
adamwoolhether
When trying to generate the protobuf .go file, I receive this error: Unknown flag: --go_opt libprotoc 3.12.3 MacOS 11.3.1 Googling ...
New
leonW
I ran this command after installing the sample application: $ cards add do something --owner Brian And got a file not found error: Fil...
New
AufHe
I’m a newbie to Rails 7 and have hit an issue with the bin/Dev script mentioned on pages 112-113. Iteration A1 - Seeing the list of prod...
New
taguniversalmachine
Hi, I am getting an error I cannot figure out on my test. I have what I think is the exact code from the book, other than I changed “us...
New
jonmac
The allprojects block listed on page 245 produces the following error when syncing gradle: “org.gradle.api.GradleScriptException: A prob...
New
New
SlowburnAZ
Getting an error when installing the dependencies at the start of this chapter: could not compile dependency :exla, "mix compile" failed...
New
dachristenson
@mfazio23 Android Studio will not accept anything I do when trying to use the Transformations class, as described on pp. 140-141. Googl...
New

Other popular topics Top

AstonJ
You might be thinking we should just ask who’s not using VSCode :joy: however there are some new additions in the space that might give V...
New
Rainer
My first contact with Erlang was about 2 years ago when I used RabbitMQ, which is written in Erlang, for my job. This made me curious and...
New
AstonJ
We have a thread about the keyboards we have, but what about nice keyboards we come across that we want? If you have seen any that look n...
New
AstonJ
There’s a whole world of custom keycaps out there that I didn’t know existed! Check out all of our Keycaps threads here: https://forum....
New
AstonJ
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me. I think the Planck and the Preonic (o...
New
AstonJ
This looks like a stunning keycap set :orange_heart: A LEGENDARY KEYBOARD LIVES ON When you bought an Apple Macintosh computer in the e...
New
PragmaticBookshelf
Author Spotlight: VM Brasseur @vmbrasseur We have a treat for you today! We turn the spotlight onto Open Source as we sit down with V...
New
DevotionGeo
I have always used antique keyboards like Cherry MX 1800 or Cherry MX 8100 and almost always have modified the switches in some way, like...
New
AstonJ
This is cool! DEEPSEEK-V3 ON M4 MAC: BLAZING FAST INFERENCE ON APPLE SILICON We just witnessed something incredible: the largest open-s...
New
Fl4m3Ph03n1x
Background Lately I am in a quest to find a good quality TTS ai generation tool to run locally in order to create audio for some videos I...
New

Sub Categories: