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