The Lost Atomic Update on Loongson CPU (jia.je)
95 points by jiegec 3 days ago
TazeTSchnitzel 4 hours ago
> 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”.
aleph_minus_one 3 hours ago
> Presumably this is a so-called “chicken bit”.
For those who are out of the loop:
> https://lwn.net/Articles/744840/
See also
> https://en.wiktionary.org/wiki/chicken_bit
(click on "quotations") for a list of scientific texts in which this term occurs.
jacquesm 35 minutes ago
Famously, the first GPS satellites had one of these, in case Einstein was wrong...
https://www.quora.com/Why-did-the-GPS-system-initially-resis...
He wasn't.
oynqr 2 hours ago
more like out of the coop
monocasa 4 hours ago
Pretty much the definition of.
Some optimization that turned out to be buggy had a disable bit in an undocumented register.