Thread

The Lost Atomic Update on Loongson CPU

131 points · 7 comments · jiegec

TazeTSchnitzel · 1790446066 · focus · HN ↗
> The fix is to set bit 13 of MCSR24 to 1. MCSR24 is an internal CSR whose function is not described in the manual. After setting this bit, the lost update no longer occurs. Testing showed the performance loss is very small: single-core performance is unaffected, and multi-core performance drops only slightly.
Presumably this is a so-called “chicken bit”.
1. aleph_minus_one · 1790448922 · focus · HN ↗
  > Presumably this is a so-called “chicken bit”.
  For those who are out of the loop:
  > <a href="https://lwn.net/Articles/744840/" rel="nofollow">https://lwn.net/Articles/744840/
  See also
  > <a href="https://en.wiktionary.org/wiki/chicken_bit" rel="nofollow">https://en.wiktionary.org/wiki/chicken_bit
  (click on "quotations") for a list of scientific texts in which this term occurs.
  1. oynqr · 1790452354 · focus · HN ↗
    more like out of the coop
  2. jacquesm · 1790459235 · focus · HN ↗
    Famously, the first GPS satellites had one of these, in case Einstein was wrong...
    <a href="https://www.quora.com/Why-did-the-GPS-system-initially-resist-using-General-relativity-corrections-and-what-changed-after-they-were-applied#AZtGs" rel="nofollow">https://www.quora.com/Why-did-the-GPS-system-initially-resis...
    He wasn't.

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