From: Ioan-Adrian Ratiu <adrian.ratiu@ni.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-rt-users@vger.kernel.org
Subject: Re: ARMv7 futex latency spike
Date: Fri, 4 Sep 2015 17:45:57 +0300 [thread overview]
Message-ID: <55E9AEA5.50504@ni.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1509041430340.15006@nanos>
On 04.09.2015 15:34, Thomas Gleixner wrote:
> On Fri, 4 Sep 2015, Ioan-Adrian Ratiu wrote:
>
>> Hello
>>
>> I wrote a C program to check jitter levels in userspace (source attached), ran
>> it on various kernels (3.14.19-rt9, 3.18.9-rt5 and 4.1.5-rt5) and on multiple
>> machines.
>
> <snip>
>
>> At .412321, "Low-prio******"'s priority is raised by "High-prio******" again,
>> as if "High-prio******" is waiting for something, but then why was it woken up
>> before?
>> * did "Low-prio******" acquire the lock again? How could it manage this feat
>> since it is already in the unlock system call?
>
> That looks like highprio is trying to acquire a kernel internal lock
> held by lowprio. The only lock which can cause this is the futex
> hashbucket lock.
>
> Now, I can see why that happens in 3.14.19-rt9, 3.18.9-rt5, but
> 4.1.5-rt5 has a fix for that. Are you sure that you that this happens
> on 4.1.5-rt5 as well?
It was a 4.1.3-rt3 build, sorry.
I will try the latest 4.1.5-rt5 and come back if this is still an issue.
Thank you,
Adrian
next prev parent reply other threads:[~2015-09-04 14:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-04 8:05 ARMv7 futex latency spike Ioan-Adrian Ratiu
2015-09-04 12:34 ` Thomas Gleixner
2015-09-04 14:45 ` Ioan-Adrian Ratiu [this message]
2015-12-11 16:34 ` Sebastian Andrzej Siewior
2015-12-14 8:54 ` Ioan-Adrian Ratiu
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