linux-kernel - Re: sched/debug: CPU hotplug operation suffers in a large cpu systems

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Message-ID: <Y1jVjX9FUuUilcjA@li-05afa54c-330e-11b2-a85c-e3f3aa0db1e9.ibm.com>
Date:   Wed, 26 Oct 2022 12:07:01 +0530
From:   Vishal Chourasia <vishalc@...ux.vnet.ibm.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        vincent.guittot@...aro.org, vschneid@...hat.com,
        srikar@...ux.vnet.ibm.com, sshegde@...ux.ibm.com,
        linuxppc-dev@...ts.ozlabs.org, ritesh.list@...il.com,
        aneesh.kumar@...ux.ibm.com
Subject: Re: sched/debug: CPU hotplug operation suffers in a large cpu systems

On Tue, Oct 18, 2022 at 01:04:40PM +0200, Greg Kroah-Hartman wrote:

> Why do you need to?  What tools require these debugfs files to be
> present?

We are not entirely sure what applications (if any) might be using this interface.

> And if you only have 7-8 files per CPU, that does not seem like a lot of
> files overall (14000-16000)?  If you only offline 1 cpu, how is removing
> 7 or 8 files a bottleneck?  Do you really offline 1999 cpus for a 2k
> system?

It's 7-8 files per domain per cpu, so, in a system with approx 2k cpus and five
domains, the total file count goes above 70k-80k files. And, when we offline 1
CPU, the entire directory is rebuilt, resulting in creation of all the files
again.

Thanks

-- vishal.c 


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