* Rich Felker <[email protected]> wrote:
> On Sat, Mar 12, 2016 at 06:00:40PM +0100, Ingo Molnar wrote:
> >
> > * Linus Torvalds <[email protected]> wrote:
> >
> > > [...]
> > >
> > > Because if that's the case, I wonder if what you really want is not
> > > "sticky
> > > signals" as much as "synchronous signals" - ie the ability to say that a
> > > signal
> > > shouldn't ever interrupt in random places, but only at well-defined
> > > points
> > > (where a system call would be one such point - are there others?)
> >
> > Yes, I had similar 'deferred signal delivery' thoughts after having written
> > up the
> > sticky signals approach, I just couldn't map all details of the semantics:
> > see the
> > 'internal libc functions' problem below.
> >
> > If we can do this approach then there's another advantage as well: this way
> > the C
> > library does not even have to poll for cancellation at syscall boundaries:
> > i.e.
> > the regular system call fast path gets faster by 2-3 instructions as well.
>
> That is not a measurable benefit. You're talking about 2-3 cycles out of 10k
> or
> more cycles (these are heavy blocking syscalls not light things like SYS_time
> or
> SYS_getpid).
Huh? The list of 'must be' cancellable system calls includes key system calls
like:
open()
close()
read() variants
write() variants
poll()
select()
which can be and often are very lightweight. The list of 'may be cancellable'
system calls includes even more lightweight system calls.
I think you are confusing 'might block' with 'will block'. Most IO operations
on a
modern kernel with modern hardware will not block!
You are scaring me ... :-(
Thanks,
Ingo
