26 Jan
2020
26 Jan
'20
6:38 p.m.
On Sun, Jan 26, 2020 at 10:29 AM Pavel Machek pavel@denx.de wrote:
po->rollover->history[prandom_u32() % ROLLOVER_HLEN] = rxhash;
victim = prandom_u32() % ROLLOVER_HLEN;/* Avoid dirtying the cache line if possible */if (READ_ONCE(history[victim]) != rxhash)WRITE_ONCE(history[victim], rxhash);Replacing simple asignment with if() is ... not nice and with all the "volatile" magic in _ONCE macros may not be win for everyone. [Actually, I don't think this is win here. This is not exactly hot path, is it?
This is a critical hot path, eg under DDOS attack.
If this is going to get more common, should we get WRITE_ONCE_NONDIRTY() macro hiding the uglyness?
Sure, but we do not add macros for stable patches, usually.
Honestly, WRITE_ONCE_NONDIRTY() looks ugly to me.
Note that the KCSAN race might be solved in another way when data_race() is available.