From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pavel Machek <pavel@ucw.cz>
Subject: Re: [RFC PATCH for 4.18 00/16] Restartable Sequences
Date: Sat, 28 Jul 2018 00:01:15 +0200
Message-ID: <20180727220115.GA18879@amd>
References: <20180602124408.8430-1-mathieu.desnoyers@efficios.com>
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To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>, "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>, Boqun Feng <boqun.feng@gmail.com>, Andy Lutomirski <luto@amacapital.net>, Dave Watson <davejwatson@fb.com>, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Paul Turner <pjt@google.com>, Andrew Morton <akpm@linux-foundation.org>, Russell King <linux@arm.linux.org.uk>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>, Andrew Hunter <ahh@google.com>, Andi Kleen <andi@firstfloor.org>, Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>, Steven Rostedt <rostedt@goodmis.org>, Josh Triplett <josh@joshtriplett.org>, Linus Torvalds <torvalds@linux-foundation.org>, Catalin Marinas <catalin.marinas@arm.com>
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Hi!

> So for instance, this turns:
>=20
>   int cpu =3D rseq_per_cpu_lock(lock, target_cpu);
>   [...]
>   rseq_per_cpu_unlock(lock, cpu);
>=20
> into
>=20
>   int cpu =3D rseq_this_cpu_lock(lock);
>   [...]
>   rseq_per_cpu_unlock(lock, cpu);
>=20
> and:
>=20
>   per_cpu_list_push(list, node, target_cpu);
>   [...]
>   per_cpu_list_pop(list, node, target_cpu);
>=20
> into
>=20
>   this_cpu_list_push(list, node, &cpu);  /* cpu is an output parameter. */
>   [...]
>   node =3D this_cpu_list_pop(list, &cpu);  /* cpu is an output parameter.=
 */
>=20
> 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.
>=20
> 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.
>=20
> Thanks for your feedback!

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

								Pavel

--=20
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo=
g.html

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