linux-kernel - Re: [patch v11 00/13] extensible prctl task isolation interface and vmstat sync

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Date:   Sat, 19 Feb 2022 16:02:10 +0800
From:   Oscar Shiang <oscar0225@...email.tw>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Nitesh Lal <nilal@...hat.com>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alex Belits <abelits@...its.com>, Peter Xu <peterx@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [patch v11 00/13] extensible prctl task isolation interface and vmstat sync

Hi Marcelo,

I tried to apply your patches to kernel v5.15.18-rt28 and measured
the latencies through oslat [1].

It turns out that the peak latency (around 100us) can drop to about 90us.
The result is impressive since I only changed the guest's kernel
instead of installing the patched kernel to both host and guest.

However, I am still curious about:
1) Why did I catch a bigger maximum latency in almost each of the
   results of applying task isolation patches? Or does it come from
   other reasons?
2) Why did we only get a 10us improvement on quiescing vmstat?

[1]: The result and the test scripts I used can be found at
https://gist.github.com/OscarShiang/8b530a00f472fd1c39f5979ee601516d#testing-task-isolation-via-oslat

Thanks,
Oscar