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List:       linux-kernel
Subject:    Re: [PATCH v3] tty: tty_io: remove hung_up_tty_fops
From:       "Paul E. McKenney" <paulmck () kernel ! org>
Date:       2024-05-01 22:32:34
Message-ID: b3b81374-a19d-4bf5-abb3-15e48c72f01a () paulmck-laptop
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On Wed, May 01, 2024 at 02:49:17PM -0700, Paul E. McKenney wrote:
> On Wed, May 01, 2024 at 02:20:35PM -0700, Linus Torvalds wrote:
> > On Wed, 1 May 2024 at 14:06, Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:

[ . . . ]

> > I'd love to see an extension where "const volatile" basically means
> > exactly that: the volatile tells the compiler that it can't
> > rematerialize by doing the load multiple times, but the "const" would
> > say that if the compiler sees two or more accesses, it can still CSE
> > them.

Except that "const volatile" already means "you cannot write to it,
and reads will not be fused".  :-/

> No promises, other than that if we don't ask, they won't say "yes".
> 
> Let me see what can be done.

From a semantics viewpoint __atomic_load_n(&x, __ATOMIC_RELAXED) would
work for loading from x.  The compilers that I tried currently do not
fuse loads, but they are allowed to do so.

Or is there something I am missing that would make this not work?
Aside from compilers not yet optimizing this case.

							Thanx, Paul

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