On 16/12/20(Wed) 23:23, Claudio Jeker wrote: > On Wed, Dec 16, 2020 at 04:50:42PM -0300, Martin Pieuchot wrote: > > [...] > > Why did we choose to use a variable over NULL? Any technical reason? > > The sleep subsytem requires a non-NULL value for ident. Changing this > seems not trivial.
I'd say this is an implementation detail, nothing prevent us to use a "private" ident value if NULL is passed to tsleep(9) :) > > I'm wondering it the locality of the variable might not matter in a > > distant future. Did you dig a bit deeper about the FreeBSD solution? > > Why did they choose a per-CPU value? > > Currently all sleep channels are hashed into IIRC 128 buckets. If all > timeouts use the same sleep channel then this queue may get overcrowded. > I guess only instrumentation and measurements will tell us how bad the > sleep queue is hashed. So using a global as sleep channel is not optimum? Would it be better to use an address on the stack? If so we could make sleep_setup() accept NULL and use 'sls' for example.
