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

yulkin
your book suggests to use Image.toByteData() to convert image to bytes, however I get the following error: "the getter ‘toByteData’ isn’t...
New
Alexandr
Hi everyone! There is an error on the page 71 in the book “Programming machine learning from coding to depp learning” P. Perrotta. You c...
New
lirux
Hi Jamis, I think there’s an issue with a test on chapter 6. I own the ebook, version P1.0 Feb. 2019. This test doesn’t pass for me: ...
New
jdufour
Hello! On page xix of the preface, it says there is a community forum "… for help if your’re stuck on one of the exercises in this book… ...
New
conradwt
First, the code resources: Page 237: rumbl_umbrella/apps/rumbl/mix.exs Note: That this file is missing. Page 238: rumbl_umbrella/app...
New
New
Charles
In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of ro...
New
a.zampa
@mfazio23 I’m following the indications of the book and arriver ad chapter 10, but the app cannot be compiled due to an error in the Bas...
New
ggerico
I got this error when executing the plot files on macOS Ventura 13.0.1 with Python 3.10.8 and matplotlib 3.6.1: programming_ML/code/03_...
New
gorkaio
root_layout: {PentoWeb.LayoutView, :root}, This results in the following following error: no “root” html template defined for PentoWeb...
New

Other popular topics Top

AstonJ
If it’s a mechanical keyboard, which switches do you have? Would you recommend it? Why? What will your next keyboard be? Pics always w...
New
AstonJ
Or looking forward to? :nerd_face:
New
brentjanderson
Bought the Moonlander mechanical keyboard. Cherry Brown MX switches. Arms and wrists have been hurting enough that it’s time I did someth...
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
Learn different ways of writing concurrent code in Elixir and increase your application's performance, without sacrificing scalability or...
New
PragmaticBookshelf
“A Mystical Experience” Hero’s Journey with Paolo Perrotta @nusco Ever wonder how authoring books compares to writing articles?...
New
AstonJ
Saw this on TikTok of all places! :lol: Anyone heard of them before? Lite:
New
AstonJ
We’ve talked about his book briefly here but it is quickly becoming obsolete - so he’s decided to create a series of 7 podcasts, the firs...
New
PragmaticBookshelf
Author Spotlight: Karl Stolley @karlstolley Logic! Rhetoric! Prag! Wow, what a combination. In this spotlight, we sit down with Karl ...
New
New

Sub Categories: