On 2021-08-26 22:36:04 [+0206], John Ogness wrote: > On 2021-08-26, Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > On 2021-08-25 15:27:54 [+0200], Frederic Weisbecker wrote: … > >> I guess making readlock writer fair is still not the plan so all I can > >> propose is to make that rwlock build-conditional. … > > It is writer fair in a sense that once a writer attempts to acquire > > the lock no new reader are allowed in. > > > > What you want is that the writer pi-boosts each reader which is what > > is not done (multi reader boost). Long ago there was an attempt to > > make this happen (I think with rwsem) but it turned out to be > > problematic. There was a workaround by only allowing one reader and > > doing PI as usual. > > This patch is essentially forcing that exact workaround for eventpoll. Frederic ended the mail with "readlock is not writer fair" so I explained that it is and he means something else and this is not not coming. I also suggested between the lines that he might try to move the reader side to RCU. > John Ogness Sebastian
