4 ms·

Ouch. Huge hit for performance.

Forbo 8y ago
From the commit message, it sounds like that might not necessarily be the case: "Note that SMT doesn't necessarily have a posive effect on performance; it highly depends on the workload. In all likelyhood it will actually slow down most workloads if you have a CPU with more than two cores."
- AHTERIX5000 8y ago
  Wonder why, because of poor SMP scalability and coarse locking? I've encountered some cases where SMT made performance worse such as with very optimized HPC libs but in general SMT can really help. Compiling projects got a nice boost when enabling HT on Intel's recent arch for example (all of this on Linux though, last time I checked OpenBSD its SMP perf was abysmal)
  - Uberphallus 8y ago
    For I/O and memory bound processes, it makes it worse, saturating further buses that are already saturated. For regular. For CPU bound, it may help or not, depending on many factors, like cache/memory contention, nature of the operations... Compilation can get boosts because while some threads are waiting for I/O others are crunching source files. Also the variety of computation is high enough so multiple threads don't overlap too much on functional unit usage. If you try to build from a filesystem in memory, you'll find way a less impressive speedup (if any).
    - AHTERIX5000 8y ago
      Yeah I've spent my time looking at perf counters and I'm aware how cache access patterns affect. But the statement was drastic enough to make me suspect there is something more OpenBSD specific going on.
mehly 8y ago
For the 12 people that run the OS.
- sctb 8y ago
  If you won't stop posting snarky one-liners we'll ban the account. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
  - nbsd4life 8y ago
    This comment finally put the puzzle pieces for why so many people seem to hate this website.
    - petee 8y ago
      A) Whom? B) Why? I can't see this flagged post, but the user in question has such quality comments as "hahahaha", "ouch", and "duhhh" -- most users here actually contribute to discussion, where as a few think this is reddit...
      - nbsd4life 8y ago
        It's extremely punishing of negative-sounding comments. People who want to call out bullshit on the orange website end up doing it on other forums so it looks like they hate it a lot.
        throwaway2048 8y ago
        Nobody here wants to look at generic comments that shit all over things, if you have something of value to say, say it, otherwise go away, nobody is going to miss you.

From the commit message, it sounds like that might not necessarily be the case: "Note that SMT doesn't necessarily have a posive effect on performance; it highly depends on the workload. In all likelyhood it will actually slow down most workloads if you have a CPU with more than two cores."

AHTERIX5000 8y ago
Wonder why, because of poor SMP scalability and coarse locking? I've encountered some cases where SMT made performance worse such as with very optimized HPC libs but in general SMT can really help. Compiling projects got a nice boost when enabling HT on Intel's recent arch for example (all of this on Linux though, last time I checked OpenBSD its SMP perf was abysmal)
- Uberphallus 8y ago
  For I/O and memory bound processes, it makes it worse, saturating further buses that are already saturated. For regular. For CPU bound, it may help or not, depending on many factors, like cache/memory contention, nature of the operations... Compilation can get boosts because while some threads are waiting for I/O others are crunching source files. Also the variety of computation is high enough so multiple threads don't overlap too much on functional unit usage. If you try to build from a filesystem in memory, you'll find way a less impressive speedup (if any).
  - AHTERIX5000 8y ago
    Yeah I've spent my time looking at perf counters and I'm aware how cache access patterns affect. But the statement was drastic enough to make me suspect there is something more OpenBSD specific going on.

mehly 8y ago

For the 12 people that run the OS.

sctb 8y ago
If you won't stop posting snarky one-liners we'll ban the account. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- nbsd4life 8y ago
  This comment finally put the puzzle pieces for why so many people seem to hate this website.
  - petee 8y ago
    A) Whom? B) Why? I can't see this flagged post, but the user in question has such quality comments as "hahahaha", "ouch", and "duhhh" -- most users here actually contribute to discussion, where as a few think this is reddit...
    - nbsd4life 8y ago
      It's extremely punishing of negative-sounding comments. People who want to call out bullshit on the orange website end up doing it on other forums so it looks like they hate it a lot.
      - throwaway2048 8y ago
        Nobody here wants to look at generic comments that shit all over things, if you have something of value to say, say it, otherwise go away, nobody is going to miss you.