* Re: system() instruction creates latency peaks
[not found] <trinity-d772b31d-ea20-4c6d-92d9-387f0952bf76-1540308456962@3c-app-mailcom-lxa13>
@ 2018-10-23 21:48 ` Jeff Epler
2018-11-08 9:53 ` Sebastian Andrzej Siewior
0 siblings, 1 reply; 2+ messages in thread
From: Jeff Epler @ 2018-10-23 21:48 UTC (permalink / raw)
To: verrodj; +Cc: linux-rt-users
Hi, I have experienced similar symptoms in realtime programs (LinuxCNC).
We have a control thread which sometimes does operations like system(),
and one or more realtime threads.
There, we changed from using system() to using posix_spawn and it
appears to have resolved the problem.
However, I don't have any explanation as to why this is the case. On
the specific version of glibc I have, posix_spawn uses vfork and system
uses clone; other syscalls like rt_sigaction are taken in the system
case but not the posix_spawn case.
Jeff
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: system() instruction creates latency peaks
2018-10-23 21:48 ` system() instruction creates latency peaks Jeff Epler
@ 2018-11-08 9:53 ` Sebastian Andrzej Siewior
0 siblings, 0 replies; 2+ messages in thread
From: Sebastian Andrzej Siewior @ 2018-11-08 9:53 UTC (permalink / raw)
To: Jeff Epler; +Cc: verrodj, linux-rt-users
On 2018-10-23 16:48:12 [-0500], Jeff Epler wrote:
> Hi, I have experienced similar symptoms in realtime programs (LinuxCNC).
> We have a control thread which sometimes does operations like system(),
> and one or more realtime threads.
>
> There, we changed from using system() to using posix_spawn and it
> appears to have resolved the problem.
>
> However, I don't have any explanation as to why this is the case. On
> the specific version of glibc I have, posix_spawn uses vfork and system
> uses clone; other syscalls like rt_sigaction are taken in the system
> case but not the posix_spawn case.
The fork() makes the whole memory COW (every write access will cause a
page fault, see mlock(2) man page).
> Jeff
Sebastian
^ permalink raw reply [flat|nested] 2+ messages in thread
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2018-10-23 21:48 ` system() instruction creates latency peaks Jeff Epler
2018-11-08 9:53 ` Sebastian Andrzej Siewior
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