From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Florian Weimer <fweimer@redhat.com>,
linux-toolchains@vger.kernel.org, Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org, stern@rowland.harvard.edu,
parri.andrea@gmail.com, boqun.feng@gmail.com, npiggin@gmail.com,
dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr,
akiyks@gmail.com, dlustig@nvidia.com, joel@joelfernandes.org,
torvalds@linux-foundation.org
Subject: Re: Control Dependencies vs C Compilers
Date: Wed, 7 Oct 2020 23:07:17 +0200 [thread overview]
Message-ID: <20201007210717.GP2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201007171107.GO29330@paulmck-ThinkPad-P72>
On Wed, Oct 07, 2020 at 10:11:07AM -0700, Paul E. McKenney wrote:
> Challenges include:
>
> o Unmarked accesses. Compilers are quite aggressive about
> moving normal code.
Which is why this thread exists :-) We wants to dis-allow lifting the
stores over our volatile-if.
> o Separately compiled code. For example, does the compiler have
> unfortunatel optimization opportunities when "volatile if"
> appears in one translation unit and the dependent stores in
> some other translation unit?
It can hardly lift anything outside a TU (barring the next point). So I
don't see how it can go wrong here. This is in fact the case with the
perf ringbuffer. The ctrl-dep lives in a different TU from the
stores.
> o LTO, as has already been mentioned in this thread.
So I would probably advocate the volatile-if to be a full sync point,
and LTO would have to preserve that.
next prev parent reply other threads:[~2020-10-07 21:07 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-06 11:47 Control Dependencies vs C Compilers Peter Zijlstra
2020-10-06 12:37 ` David Laight
2020-10-06 12:49 ` Willy Tarreau
2020-10-06 13:31 ` Peter Zijlstra
2020-10-06 14:23 ` stern
2020-10-06 14:43 ` Peter Zijlstra
2020-10-06 15:16 ` Nick Clifton
2020-10-06 15:37 ` David Laight
2020-10-06 15:50 ` Paul E. McKenney
2020-10-06 16:10 ` Willy Tarreau
2020-10-06 16:22 ` David Laight
2020-10-06 16:31 ` Paul E. McKenney
2020-10-06 15:07 ` David Laight
2020-10-06 21:20 ` Florian Weimer
2020-10-07 9:32 ` Peter Zijlstra
2020-10-07 10:20 ` Florian Weimer
2020-10-07 11:50 ` Peter Zijlstra
2020-10-07 17:11 ` Paul E. McKenney
2020-10-07 21:07 ` Peter Zijlstra [this message]
2020-10-07 21:20 ` Paul E. McKenney
2020-10-07 10:30 ` Willy Tarreau
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