Re: user-space concurrent pipe buffer scheduler interactions

[Michael Clark]

On 4/4/24 09:57, Linus Torvalds wrote:
> On Wed, 3 Apr 2024 at 13:52, Michael Clark <michael@xxxxxxxxxxxxxxxx> wrote:
> > On 4/4/24 05:56, Linus Torvalds wrote:
> > > On Tue, 2 Apr 2024 at 13:54, Michael Clark <michael@xxxxxxxxxxxxxxxx> wrote:
> > > > I am working on a low latency cross-platform concurrent pipe buffer
> > > > using C11 threads and atomics.
> > >
> > > You will never get good performance doing spinlocks in user space
> > > unless you actually tell the scheduler about the spinlocks, and have
> > > some way to actually sleep on contention.
> > >
> > > Which I don't see you as having.
> >
> > We can work on this.
>
> It's been tried.
>
> Nobody ever found a use-case that is sufficiently convincing, but see
> the write-up at
>
>     https://lwn.net/Articles/944895/

It's certainly interesting!

I wouldn't throw in the towel so soon until folks tried a bit harder. 
Even if we can't make it faster it would be neat to have an Austin Group 
meeting to give us user-space devels a waitlist_t so we don't hit that 
brain damaged deadlocky cond_wait foot-gun and realize its totally 
broken and that we must use cond_timedwait with some stupid delay until 
we can recheck the condition again in user-space in our "portable code".

Michael.