4 ms·

You probably mean minimal latency, not maximum throughput. GC generally has higher throughput at the cost of latency and higher peak memory usage. :)

z92 10y ago
Parallel GC's throughput is limited by how hard the parallel thread is working as described in the article and which was the point.
- chadaustin 10y ago
  But he's comparing to reference counting, where you pay a substantial throughput penalty round-tripping to RAM (especially if atomic) and don't get the benefit of a bump allocator.
kartickv 10y ago
I've seen it repeated many times that GC has higher latency, but is there a benchmark? Imagine writing a Mac app, once with refcounting, and once with GC, and seeing which one has the longer pause time. I can think of cases where GC has better latency, like deallocating a huge linked list. That will introduce a higher latency with refcounting and with manual deletion (like C) compared to GC, where the main thread doesn't need to block while traversing the list. Or does such a case not happen much in practice?
- iainmerrick 10y ago
  You mainly notice it in mobile apps, since you want silky smooth 60fps scrolling there. A pause longer than 5 or 10ms can easily cause you to drop a frame.
  - kartickv 10y ago
    Hard to attribute that to GC.
    - iainmerrick 10y ago
      Why hard? On Android, the GC will print a log entry telling you how long it took! In my experience, aside from badly-written algorithms that just do too much work on the wrong thread, the main causes of momentary glitches are GC and I/O. Unfortunately you have limited control over those in application code (just using too much memory can cause some I/O churn). On mobile, the GPU drivers are often badly written and will give you random hiccups that can ultimately be traced back to I/O. Not to turn this into an Apple vs Android battle, I hope, but I think this is an important point that is often overlooked -- Apple's hardware and software designs are really well-targeted to minimize those kind of glitches. They don't use GC and they always use very fast (AKA expensive) flash memory. So whatever else their flaws, Apple devices tend to have smoothly-animated UIs.
iainmerrick 10y ago
Oops, you're right! I think I had in mind something like "guaranteed throughput" but "consistent low latency" is definitely a better way to put it.

z92 10y ago

Parallel GC's throughput is limited by how hard the parallel thread is working as described in the article and which was the point.

chadaustin 10y ago
But he's comparing to reference counting, where you pay a substantial throughput penalty round-tripping to RAM (especially if atomic) and don't get the benefit of a bump allocator.

kartickv 10y ago

I've seen it repeated many times that GC has higher latency, but is there a benchmark? Imagine writing a Mac app, once with refcounting, and once with GC, and seeing which one has the longer pause time. I can think of cases where GC has better latency, like deallocating a huge linked list. That will introduce a higher latency with refcounting and with manual deletion (like C) compared to GC, where the main thread doesn't need to block while traversing the list. Or does such a case not happen much in practice?

iainmerrick 10y ago
You mainly notice it in mobile apps, since you want silky smooth 60fps scrolling there. A pause longer than 5 or 10ms can easily cause you to drop a frame.
- kartickv 10y ago
  Hard to attribute that to GC.
  - iainmerrick 10y ago
    Why hard? On Android, the GC will print a log entry telling you how long it took! In my experience, aside from badly-written algorithms that just do too much work on the wrong thread, the main causes of momentary glitches are GC and I/O. Unfortunately you have limited control over those in application code (just using too much memory can cause some I/O churn). On mobile, the GPU drivers are often badly written and will give you random hiccups that can ultimately be traced back to I/O. Not to turn this into an Apple vs Android battle, I hope, but I think this is an important point that is often overlooked -- Apple's hardware and software designs are really well-targeted to minimize those kind of glitches. They don't use GC and they always use very fast (AKA expensive) flash memory. So whatever else their flaws, Apple devices tend to have smoothly-animated UIs.

iainmerrick 10y ago

Oops, you're right! I think I had in mind something like "guaranteed throughput" but "consistent low latency" is definitely a better way to put it.