On Sun, 2025-02-09 at 13:57 -0800, Linus Torvalds wrote: > > So on x86, both read and write barriers are complete no-ops, because > all reads are ordered, and all writes are ordered. Given that this thread started with a reference to rdtsc, it may be worth keeping in mind that rdtsc reads themselves do not always appear to be ordered. Paul and I spotted some occasionaly "backwards TSC values" from the CSD lock instrumentation code, which went away when using ordered TSC reads: https://lkml.iu.edu/hypermail/linux/kernel/2410.1/03202.html I guess maybe a TSC read does not follow all the same rules as a memory read, sometimes? -- All Rights Reversed.
