On Tue, Jun 08, 2021 at 03:06:48PM +0300, Andrey Semashev wrote: > On 6/8/21 2:13 PM, Greg KH wrote: > > On Tue, Jun 08, 2021 at 02:03:50PM +0300, Andrey Semashev wrote: > > > On 6/8/21 4:25 AM, Nicholas Piggin wrote: > > > > > > > > Are shared pthread mutexes using existing pthread APIs that are today > > > > implemented okay with futex1 system call a good reason to constrain > > > > futex2 I wonder? Or do we have an opportunity to make a bigger change > > > > to the API so it suffers less from non deterministic latency (for > > > > example)? > > > > > > If futex2 is not able to cover futex1 use cases then it cannot be viewed as > > > a replacement. In the long term this means futex1 cannot be deprecated and > > > has to be maintained. My impression was that futex1 was basically > > > unmaintainable(*) and futex2 was an evolution of futex1 so that users of > > > futex1 could migrate relatively easily and futex1 eventually removed. Maybe > > > my impression was wrong, but I would like to see futex2 as a replacement and > > > extension of futex1, so the latter can be deprecated at some point. > > > > You can never delete a kernel system call, so even if you "deprecate" > > it, it still needs to be supported for forever. > > If I'm not mistaken, some syscalls were dropped from kernel in the past, > after it was established they are no longer used. So it is not impossible, > though might be more difficult specifically with futex. Those syscalls were all "compatible with other obsolete operating system" syscalls from what I remember. You can still run binaries built in 1995 just fine on your system today (I have a few around here somewhere...) Thinking that you can drop futex() in the next 10+ years is very wishful thinking given just how slow userspace applications are ever updated, sorry. greg k-h
