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From: Pavel Machek <pavel@ucw.cz>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Florian Weimer <fweimer@redhat.com>, carlos <carlos@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	libc-alpha <libc-alpha@sourceware.org>
Subject: Re: Restartable Sequences system call merged into Linux
Date: Thu, 14 Jun 2018 14:27:59 +0200	[thread overview]
Message-ID: <20180614122759.GB8798@amd> (raw)
In-Reply-To: <417742741.11550.1528821084084.JavaMail.zimbra@efficios.com>

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On Tue 2018-06-12 12:31:24, Mathieu Desnoyers wrote:
> ----- On Jun 12, 2018, at 9:11 AM, Florian Weimer fweimer@redhat.com wrote:
> 
> > On 06/11/2018 10:04 PM, Mathieu Desnoyers wrote:
> >> ----- On Jun 11, 2018, at 3:55 PM, Florian Weimer fweimer@redhat.com wrote:
> >> 
> >>> On 06/11/2018 09:49 PM, Mathieu Desnoyers wrote:
> >>>> It should be noted that there can be only one rseq TLS area registered per
> >>>> thread,
> >>>> which can then be used by many libraries and by the executable, so this is a
> >>>> process-wide (per-thread) resource that we need to manage carefully.
> >>>
> >>> Is it possible to resize the area after thread creation, perhaps even
> >>> from other threads?
> >> 
> >> I'm not sure why we would want to resize it. The per-thread area is fixed-size.
> >> Its layout is here: include/uapi/linux/rseq.h: struct rseq
> > 
> > Looks I was mistaken and this is very similar to the robust mutex list.
> > 
> > Should we treat it the same way?  Always allocate it for each new thread
> > and register it with the kernel?
> 
> That would be an efficient way to do it, indeed. There is very little
> performance overhead to have rseq registered for all threads, whether or
> not they intend to run rseq critical sections.

People with slow / low memory machines would prefer not to see
overhead they don't need...

> I have a few possible approaches in mind (feel free to suggest other
> options):
> 
> A) glibc exposes a strong __rseq_abi TLS symbol:
> 
>    - should ideally *not* be global-dynamic for performance reasons,
>    - registration to kernel can either be handled explicitly by requiring
>      application or libraries to call an API, or implicitly at thread
>      creation,

...so I'd prefer explicit API call.

> B) librseq.so exposes a strong __rseq_abi symbol:

Works for me.
									Pavel

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

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  parent reply	other threads:[~2018-06-14 12:28 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-11 19:49 Mathieu Desnoyers
2018-06-11 19:55 ` Florian Weimer
2018-06-11 20:04   ` Mathieu Desnoyers
2018-06-12 13:11     ` Florian Weimer
2018-06-12 16:31       ` Mathieu Desnoyers
2018-06-13  8:21         ` Florian Weimer
2018-06-14 12:27         ` Pavel Machek [this message]
2018-06-14 13:01           ` Mathieu Desnoyers
2018-06-14 13:25             ` Pavel Machek
2018-06-14 13:32               ` Florian Weimer
2018-06-14 13:46                 ` Mathieu Desnoyers
2018-06-15  5:10                   ` Florian Weimer
2018-06-15 17:44                     ` Mathieu Desnoyers
2018-06-14 13:38               ` Mathieu Desnoyers
2018-06-14 13:49                 ` Pavel Machek
2018-06-14 14:00                   ` Florian Weimer
2018-06-14 14:36                     ` Mathieu Desnoyers
2018-06-14 14:41                       ` Florian Weimer
2018-06-14 15:09                         ` Mathieu Desnoyers
2018-06-15  5:09             ` Florian Weimer
2018-06-15 17:50               ` Mathieu Desnoyers
2018-06-15  5:07           ` Florian Weimer
2018-06-13 11:48 ` Heiko Carstens
2018-06-13 16:14   ` Mathieu Desnoyers
2018-06-13 19:53     ` Mathieu Desnoyers

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