linux-kernel - Re: [RFC PATCH for 4.18 00/16] Restartable Sequences

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Message-ID: <20180727220115.GA18879@amd>
Date:   Sat, 28 Jul 2018 00:01:15 +0200
From:   Pavel Machek <pavel@....cz>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [RFC PATCH for 4.18 00/16] Restartable Sequences

Hi!

> So for instance, this turns:
> 
>   int cpu = rseq_per_cpu_lock(lock, target_cpu);
>   [...]
>   rseq_per_cpu_unlock(lock, cpu);
> 
> into
> 
>   int cpu = rseq_this_cpu_lock(lock);
>   [...]
>   rseq_per_cpu_unlock(lock, cpu);
> 
> and:
> 
>   per_cpu_list_push(list, node, target_cpu);
>   [...]
>   per_cpu_list_pop(list, node, target_cpu);
> 
> into
> 
>   this_cpu_list_push(list, node, &cpu);  /* cpu is an output parameter. */
>   [...]
>   node = this_cpu_list_pop(list, &cpu);  /* cpu is an output parameter. */
> 
> Eventually integrating cpu_opv or some alternative will allow passing
> the cpu number as parameter rather than requiring the algorithm to work
> on the current CPU.
> 
> The second effect of not having the cpu_opv fallback is that
> line and instruction single-stepping with a debugger transforms rseq
> critical sections based on retry loops into never-ending loops.
> Debuggers need to use the __rseq_table section to skip those critical
> sections in order to correctly behave when single-stepping a thread
> which uses rseq in a retry loop. However, applications which use an
> alternative fallback method rather than retrying on rseq fast-path abort
> won't be affected by this kind of single-stepping issue.
> 
> Thanks for your feedback!

Would it make sense to include Documentation/ patch? I guess at least
manpage describing the syscall will be needed....

								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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