From: Ingo Molnar <mingo@kernel.org>
To: Rich Felker <dalias@libc.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Borislav Petkov <bp@alien8.de>,
"musl@lists.openwall.com" <musl@lists.openwall.com>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers
Date: Sat, 12 Mar 2016 19:48:36 +0100 [thread overview]
Message-ID: <20160312184836.GA17707@gmail.com> (raw)
In-Reply-To: <20160312180531.GD9349@brightrain.aerifal.cx>
* Rich Felker <dalias@libc.org> wrote:
> On Sat, Mar 12, 2016 at 06:00:40PM +0100, Ingo Molnar wrote:
> >
> > * Linus Torvalds <torvalds@linux-foundation.org> 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
next prev parent reply other threads:[~2016-03-12 18:48 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-09 1:24 [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Andy Lutomirski
2016-03-09 8:56 ` Ingo Molnar
2016-03-09 11:34 ` [musl] " Szabolcs Nagy
2016-03-09 11:40 ` Szabolcs Nagy
2016-03-09 19:47 ` Linus Torvalds
2016-03-09 20:57 ` Andy Lutomirski
2016-03-09 21:26 ` Linus Torvalds
2016-03-10 10:57 ` Ingo Molnar
2016-03-10 3:34 ` Rich Felker
2016-03-10 11:16 ` Ingo Molnar
2016-03-10 16:41 ` Rich Felker
2016-03-10 18:03 ` Ingo Molnar
2016-03-10 23:28 ` Rich Felker
2016-03-11 0:18 ` Szabolcs Nagy
2016-03-11 0:48 ` Rich Felker
2016-03-11 1:14 ` Andy Lutomirski
2016-03-11 1:39 ` Szabolcs Nagy
2016-03-11 1:49 ` Szabolcs Nagy
2016-03-11 1:55 ` Rich Felker
2016-03-11 9:33 ` Ingo Molnar
2016-03-11 11:39 ` Szabolcs Nagy
2016-03-11 19:27 ` Linus Torvalds
2016-03-11 19:30 ` Andy Lutomirski
2016-03-11 19:39 ` Linus Torvalds
2016-03-11 19:44 ` Linus Torvalds
2016-03-12 17:05 ` Ingo Molnar
2016-03-12 18:10 ` Rich Felker
2016-03-12 17:00 ` Ingo Molnar
2016-03-12 18:05 ` Rich Felker
2016-03-12 18:48 ` Ingo Molnar [this message]
2016-03-12 19:08 ` Rich Felker
2016-03-12 17:08 ` Ingo Molnar
2016-03-09 17:58 ` Andy Lutomirski
2016-03-09 21:19 ` Andy Lutomirski
2016-03-12 18:13 ` Andy Lutomirski
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