From: Marcelo Tosatti <mtosatti@redhat.com>
To: Christoph Lameter <cl@gentwo.de>
Cc: Aaron Tomlin <atomlin@atomlin.com>,
Frederic Weisbecker <frederic@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 3/5] mm/vmstat: use cmpxchg loop in cpu_vm_stats_fold
Date: Fri, 3 Feb 2023 15:52:14 -0300 [thread overview]
Message-ID: <Y91X3hA5i7FQJwEo@tpad> (raw)
In-Reply-To: <5615572-974e-74cc-6c34-1de618b777cf@gentwo.de>
On Fri, Feb 03, 2023 at 10:34:22AM +0100, Christoph Lameter wrote:
> On Thu, 2 Feb 2023, Marcelo Tosatti wrote:
>
> > > I thought you would only run this while the kernel is not active on the
> > > remote cpu? Then you dont need any cmpxchg and you can leave the function
> > > as is.
> >
> > The remote cpu can enter kernel mode while this function executes.
>
> Isnt there some lock/serializtion to stall the kernel until you are done?
Not that i know of. Anyway, an additional datapoint is:
"Software defined PLC"
(https://www.redhat.com/en/blog/software-defined-programmable-logic-controller-introduction),
applications
can perform system calls in their time sensitive loop.
One example of an opensource software is OpenPLC.
One would like to avoid interruptions for those cases as well.
> > There is no mode which indicates userspace cannot enter the kernel.
>
> There are lot of thinngs that happen upon entry to the kernel. I would
> hope that you can do something there. Scheduler?
The use-case in question is with isolation, where a CPU is dedicated
to a single task. So the scheduler should not be an issue.
next prev parent reply other threads:[~2023-02-03 18:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-01 19:50 [PATCH 0/5] fold per-CPU vmstats remotely Marcelo Tosatti
2023-02-01 19:50 ` [PATCH 1/5] mm/vmstat: remove remote node draining Marcelo Tosatti
2023-02-01 19:50 ` [PATCH 2/5] mm/vmstat: switch counter modification to cmpxchg Marcelo Tosatti
2023-02-01 19:50 ` [PATCH 3/5] mm/vmstat: use cmpxchg loop in cpu_vm_stats_fold Marcelo Tosatti
2023-02-02 14:38 ` Christoph Lameter
2023-02-02 15:54 ` Marcelo Tosatti
2023-02-03 9:34 ` Christoph Lameter
2023-02-03 18:52 ` Marcelo Tosatti [this message]
2023-02-06 9:42 ` Christoph Lameter
2023-02-06 19:10 ` Marcelo Tosatti
2023-02-06 19:19 ` Matthew Wilcox
2023-02-01 19:50 ` [PATCH 4/5] mm/vmstat: switch vmstat shepherd to flush per-CPU counters remotely Marcelo Tosatti
2023-02-01 19:50 ` [PATCH 5/5] mm/vmstat: refresh stats remotely instead of via work item Marcelo Tosatti
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