linux-kernel - Re: [RFC 0/3] tools/memory-model: Add litmus tests for atomic APIs

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Date:   Sun, 16 Feb 2020 11:16:50 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Paul E. McKenney" <paulmck@...nel.org>
cc:     Boqun Feng <boqun.feng@...il.com>, <linux-kernel@...r.kernel.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Jonathan Corbet <corbet@....net>, <linux-arch@...r.kernel.org>,
        <linux-doc@...r.kernel.org>
Subject: Re: [RFC 0/3] tools/memory-model: Add litmus tests for atomic APIs

On Sun, 16 Feb 2020, Paul E. McKenney wrote:

> On Sun, Feb 16, 2020 at 01:43:45PM +0800, Boqun Feng wrote:
> > On Sat, Feb 15, 2020 at 07:25:50AM -0800, Paul E. McKenney wrote:
> > > On Fri, Feb 14, 2020 at 10:27:44AM -0500, Alan Stern wrote:
> > > > On Fri, 14 Feb 2020, Boqun Feng wrote:
> > > > 
> > > > > A recent discussion raises up the requirement for having test cases for
> > > > > atomic APIs:
> > > > > 
> > > > > 	https://lore.kernel.org/lkml/20200213085849.GL14897@hirez.programming.kicks-ass.net/
> > > > > 
> > > > > , and since we already have a way to generate a test module from a
> > > > > litmus test with klitmus[1]. It makes sense that we add more litmus
> > > > > tests for atomic APIs into memory-model.
> > > > 
> > > > It might be worth discussing this point a little more fully.  The 
> > > > set of tests in tools/memory-model/litmus-tests/ is deliberately rather 
> > > > limited.  Paul has a vastly more expansive set of litmus tests in a 
> > > > GitHub repository, and I am doubtful about how many new tests we want 
> > > > to keep in the kernel source.
> > > 
> > > Indeed, the current view is that the litmus tests in the kernel source
> > > tree are intended to provide examples of C-litmus-test-language features
> > > and functions, as opposed to exercising the full cross-product of
> > > Linux-kernel synchronization primitives.
> > > 
> > > For a semi-reasonable subset of that cross-product, as Alan says, please
> > > see https://github.com/paulmckrcu/litmus.
> > > 
> > > For a list of the Linux-kernel synchronization primitives currently
> > > supported by LKMM, please see tools/memory-model/linux-kernel.def.
> > > 
> > 
> > So how about I put those atomic API tests into a separate directory, say
> > Documentation/atomic/ ?
> > 
> > The problem I want to solve here is that people (usually who implements
> > the atomic APIs for new archs) may want some examples, which can help
> > them understand the API requirements and test the implementation. And
> > litmus tests are the perfect tool here (given that them can be
> > translated to test modules with klitmus). And I personally really think
> > this is something the LKMM group should maintain, that's why I put them
> > in the tools/memory-model/litmus-tests/. But I'm OK if we end up
> > deciding those should be put outside that directory.
> 
> Good point!
> 
> However, we should dicuss this with the proposed beneficiaries, namely
> the architecture maintainers.  Do they want it?  If so, where would
> they like it to be?  How should it be organized?
> 
> In the meantime, I am more than happy to accept litmus tests into the
> github archive.
> 
> So how would you like to proceed?

I think it makes sense to put Boqun's tests under Documentation/ rather
than tools/.  After all, their point is to document the memory model's
requirements for operations on atomic_t's.  They aren't meant to be
examples or demos showing how to use herd or write litmus tests.

Alan