From: John Kacur <jkacur@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: Daniel Wagner <wagi@monom.org>,
linux-rt-users@vger.kernel.org,
Clark Williams <williams@redhat.com>,
Daniel Wagner <dwagner@suse.de>
Subject: Re: [PATCH] rt-tests: Drop use_current_cpuset() check
Date: Wed, 17 Mar 2021 11:47:51 -0400 (EDT) [thread overview]
Message-ID: <dab375fb-b2df-fd6c-3931-cd24d4fa26a@redhat.com> (raw)
In-Reply-To: <20210317152100.GL395976@xz-x1>
On Wed, 17 Mar 2021, Peter Xu wrote:
> On Wed, Mar 17, 2021 at 11:08:31AM -0400, John Kacur wrote:
> >
> >
> > On Wed, 17 Mar 2021, Peter Xu wrote:
> >
> > > Hi, Daniel,
> > >
> > > On Wed, Mar 17, 2021 at 08:49:03AM +0100, Daniel Wagner wrote:
> > > > On Tue, Mar 16, 2021 at 04:07:05PM -0400, Peter Xu wrote:
> > > > > I think what I'm missing is why we had such a restriction. Quotting from the
> > > > > commit ID:
> > > >
> > > > IIRC, the current behavior allows the process to be placed into a cgroup
> > > > with a subset of CPUs and you just can do 'cyclictest -a -t'. Process
> > > > should not ignore external configuration. That's my whole point here.
> > >
> > > In that case again I think a sane solution is not to check the cpu list in
> > > every single tool we use, because even if we do that for all tools in rt-teets
> > > repo, we can't guarantee to have this check for the rest tools to not ignore
> > > this restriction.
> > >
> > > A simple example is: what if the user specified "taskset -c $CPU cyclictest -a
> > > $CPU -t 1 ..." where $CPU is not in the allowed list of current bash? As long
> > > as the taskset would work the so-called "environment" will be changed before
> > > even loading cyclictest.
> > >
> > > If you see that's the point I said we should fail at the same check point of
> > > sched_setaffinity() rather than checking it explicitly in the tool, because
> > > if we want a real-world restriction that's the only place I think it's possible..
> > >
> > > But I'm not a cgroup/container guy, please correct me if I understood.
> > >
> > > --
> > > Peter Xu
> > >
> > >
> >
> > When cyclictest and friends were originally written, we had this view
> > point that we "owned" the whole machine, and didn't have any restrictions
> > on where to schedule. As machines grew in size, and we added numa
> > awareness, and cgroups became more prominent we added this code that tried
> > to schedule according to the ill-defined environment that we found
> > ourselves in.
> >
> > As Peter points out we may have restricted ourselves more than is
> > necessary, and can rely a bit more on the operating system to restrict us.
> > On the otherhand using taskset is an easy workaround if the current code
> > is to restrictive.
> >
> > Because we can use taskset and things are working well otherwise I don't
> > see this as super urgent, but I am willing to revisit this code and make
> > it less restrictive if that makes sense.
> >
> > I also am not a cgroup / container person, and would like to play around
> > with this a bit more before we make some decisions on which direction to
> > go in.
> >
> > Does that make sense to everyone?
>
> Sure thing on my side. No bug reported so far this time, so I'll wait at least
> until then :) I just don't know why it's not hit just like oslat since I don't
> see a difference. When I fixed the oslat thing, I thought cyclictest didn't
> have such issue for some reason so I didn't consider to touch it at all. But
> when yesterday I rerun some tests I see this issue on rhel8, hence this patch.
>
> Thanks,
>
> --
> Peter Xu
>
>
Thanks Peter - I appreciate it!
John
next prev parent reply other threads:[~2021-03-17 15:49 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 19:37 [PATCH] rt-tests: Drop use_current_cpuset() check Peter Xu
2021-03-16 8:18 ` Daniel Wagner
2021-03-16 20:07 ` Peter Xu
2021-03-17 7:49 ` Daniel Wagner
2021-03-17 12:51 ` Peter Xu
2021-03-17 15:08 ` John Kacur
2021-03-17 15:21 ` Peter Xu
2021-03-17 15:47 ` John Kacur [this message]
2021-03-17 17:20 ` Daniel Wagner
2021-03-17 16:40 ` Ahmed S. Darwish
2021-03-17 17:15 ` Daniel Wagner
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