From: Jan Kiszka <jan.kiszka@siemens.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: lttng-dev <lttng-dev@lists.lttng.org>,
paulmck <paulmck@kernel.org>, Xenomai <xenomai@xenomai.org>
Subject: Re: Using lttng-ust with xenomai
Date: Fri, 22 Nov 2019 18:36:54 +0100 [thread overview]
Message-ID: <f25860cc-e5b6-ae89-1a21-b85093291398__3246.15436127118$1574444251$gmane$org@siemens.com> (raw)
In-Reply-To: <480743920.929.1574442078799.JavaMail.zimbra@efficios.com>
On 22.11.19 18:01, Mathieu Desnoyers wrote:
>>>>
>>>> ## membarrier syscall
>>>>
>>>> I haven't got an explanation yet, but I believe this syscall does
>>>> nothing to xenomai threads (each has a shadow linux thread, that is
>>>> *idle* when the xenomai thread is active).
>>>
>>> That's indeed a good point. I suspect membarrier may not send any IPI
>>> to Xenomai threads (that would have to be confirmed). I suspect the
>>> latency introduced by this IPI would be unwanted.
>>
>> Is an "IPI" a POSIX signal here? Or are real IPI that delivers an
>> interrupt to Linux on another CPU? The latter would still be possible,
>> but it would be delayed until all Xenomai threads on that core eventual
>> took a break (which should happen a couple of times per second under
>> normal conditions - 100% RT load is an illegal application state).
>
> I'm talking about a real in-kernel IPI (as in inter-processor interrupt).
> However, the way sys_membarrier detects which CPUs should receive that IPI
> is by iterating on all cpu runqueues, and figure out which CPU is currently
> running a thread which uses the same mm as the sys_membarrier caller
> (for the PRIVATE membarrier commands).
>
> So I suspect that the Xenomai thread is really not within the Linux scheduler
> runqueue when it runs.
True. Xenomai first suspends the RT thread's Linux shadow and then kicks
the Xenomai scheduler to interrupt Linux (and schedule in the RT
thread). So, from a remote Linux perspective, something else will be
running at this point.
Jan
--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux
next prev parent reply other threads:[~2019-11-22 17:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CADYdroN-i9yrpd-wjPSW36GUptRV+kOCJT=Yv6+Z5sCVBmo_SQ@mail.gmail.com>
2019-11-22 15:42 ` Using lttng-ust with xenomai Mathieu Desnoyers
[not found] ` <2012667816.853.1574437363737.JavaMail.zimbra@efficios.com>
2019-11-22 15:52 ` Jan Kiszka
[not found] ` <4aab99be-5451-4582-f75d-7637614b1d37@siemens.com>
2019-11-22 17:01 ` Mathieu Desnoyers
[not found] ` <480743920.929.1574442078799.JavaMail.zimbra@efficios.com>
2019-11-22 17:36 ` Jan Kiszka [this message]
2019-11-22 17:44 ` Norbert Lange
[not found] ` <CADYdroOh+T8pOcNBW74KSMfCh--ujD8L3_G96LWR1migpsUq0g@mail.gmail.com>
2019-11-22 17:52 ` Jan Kiszka
[not found] ` <63a51fa5-db96-9cf9-0eb3-51954ebf98f4@siemens.com>
2019-11-22 18:01 ` Norbert Lange
[not found] ` <CADYdroP+H3DiqCaH9o1jHxAurh_2YG_p7MK4H2kFqSoTCV0w6A@mail.gmail.com>
2019-11-22 18:07 ` Jan Kiszka
[not found] ` <a2036ba8-c22a-e549-b68d-35524ee7f9a9@siemens.com>
2019-11-22 21:38 ` Norbert Lange
2019-11-22 19:00 ` Mathieu Desnoyers
[not found] ` <2088324778.1063.1574449205629.JavaMail.zimbra@efficios.com>
2019-11-22 19:57 ` Norbert Lange
[not found] ` <CADYdroM7acqfMym1sUbwaa773SLSzHPSni9uRxiLZbbHtteLug@mail.gmail.com>
2019-11-22 20:15 ` Mathieu Desnoyers
[not found] ` <547908110.1420.1574453756850.JavaMail.zimbra@efficios.com>
2019-11-22 21:27 ` [lttng-dev] " Norbert Lange via Xenomai
2019-11-22 17:55 ` Norbert Lange
[not found] ` <CADYdroNGcY6adA5cGTzwzsKqO7+iuWts9k8Haz8k3HSvzQfc=g@mail.gmail.com>
2019-11-22 19:03 ` Mathieu Desnoyers
[not found] ` <1007669875.1091.1574449410739.JavaMail.zimbra@efficios.com>
2019-11-22 20:04 ` Norbert Lange
2019-11-22 9:14 Norbert Lange
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