On 2/28/20 1:25 PM, Thomas Gleixner wrote:
Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
On Fri, Feb 28, 2020 at 08:07:17PM +0100, Peter Zijlstra wrote:
So I have a problem with this vector layout, it doesn't allow for
per-futex flags, and esp. with that multi-size futex support that
becomes important, but also with the already extand private/shared and
wait_bitset flags this means you cannot have a vector with mixed wait
types.
Alternatively, we throw the entire single-syscall futex interface under
the bus and design a bunch of new syscalls that are natively vectored or
something.
Thomas mentioned something like that, the problem is, ofcourse, that we
then want to fix a whole bunch of historical ills, and the probmem
becomes much bigger.
We keep piling features on top of an interface and mechanism which is
fragile as hell and horrible to maintain. Adding vectoring, multi size
and whatever is not making it any better.
There is also the long standing issue with NUMA, which we can't address
with the current pile at all.
So I'm really advocating that all involved parties sit down ASAP and
hash out a new and less convoluted mechanism where all the magic new
features can be addressed in a sane way so that the 'F' in Futex really
only means Fast and not some other word starting with 'F'.
Are you specifically talking about the interface, or the mechanism
itself? Would you be OK with a new syscall that calls into the same code
as this patch? It does seem like that's what we want, so if we rewrote a
mechanism I'm not convinced it would come out any different. But, the
interface itself seems fair-game to rewrite, as the current futex
syscall is turning into an ioctl of sorts.
This solves a real problem with a real usecase; so I'd like to stay
practical and not go into deeper issues like solving NUMA support for
all of futex in the interest of users waiting at the other end. Can you
point us to your preferred approach just for the scope of what we're
trying to accomplish?
Thanks,
tglx
