Comment by pajko

15 days ago

Timestamps should NOT be compared like this. Exactly this is why time_before() or time_after() exist.

https://elixir.bootlin.com/linux/v6.15.7/source/include/linu...

5 comments

pajko

Offtopic...

    * Do this with "<0" and ">=0" to only test the sign of the result. A
    * good compiler would generate better code (and a really good compiler
    * wouldn't care). Gcc is currently neither.

It's funny the love-hate relationship the Linux kernel has with GCC. It's the only supported compiler[1], and yet...

[1] can Clang fully compile Linux yet? I haven't followed the updates in a while.

rwmj 15 days ago

To be fair this comment predates git history (before 2005) when GCC wasn't a very good compiler. The kernel developers at one point were sticking with a specific version of GCC because later versions would miscompile the kernel. Clang didn't exist then.
GCC is a different beast and far better nowadays.
EvgeniyZh 15 days ago

Yes it can [1].
https://docs.kernel.org/kbuild/llvm.html

Joker_vD 15 days ago

Do I understand it correctly that the logic is that if timestamp B is above timestamp A, but the difference is more than half of the unsigned range, B is considered to happen before A?

rcxdude 15 days ago

Yes. When the timestamps wrap it's fundamentally ambiguous, but this will be correct unless the timestamps are very far apart (and the failure mode is more benign: a really long time difference being considered shorter is better than all time differences being considered zero after the timestamp wraps).