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From: Vishal Chourasia <vishalc@linux.vnet.ibm.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, mingo@redhat.com,
	vincent.guittot@linaro.org, vschneid@redhat.com,
	srikar@linux.vnet.ibm.com, sshegde@linux.ibm.com,
	linuxppc-dev@lists.ozlabs.org, ritesh.list@gmail.com,
	aneesh.kumar@linux.ibm.com
Subject: Re: sched/debug: CPU hotplug operation suffers in a large cpu systems
Date: Wed, 26 Oct 2022 12:07:01 +0530	[thread overview]
Message-ID: <Y1jVjX9FUuUilcjA@li-05afa54c-330e-11b2-a85c-e3f3aa0db1e9.ibm.com> (raw)
In-Reply-To: <Y06ISBWhJflnV+NI@kroah.com>

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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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WARNING: multiple messages have this Message-ID (diff)
From: Vishal Chourasia <vishalc@linux.vnet.ibm.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: ritesh.list@gmail.com, vschneid@redhat.com,
	vincent.guittot@linaro.org, srikar@linux.vnet.ibm.com,
	Peter Zijlstra <peterz@infradead.org>,
	aneesh.kumar@linux.ibm.com, linux-kernel@vger.kernel.org,
	sshegde@linux.ibm.com, mingo@redhat.com,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: sched/debug: CPU hotplug operation suffers in a large cpu systems
Date: Wed, 26 Oct 2022 12:07:01 +0530	[thread overview]
Message-ID: <Y1jVjX9FUuUilcjA@li-05afa54c-330e-11b2-a85c-e3f3aa0db1e9.ibm.com> (raw)
In-Reply-To: <Y06ISBWhJflnV+NI@kroah.com>

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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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  reply	other threads:[~2022-10-26  6:38 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-17 13:10 sched/debug: CPU hotplug operation suffers in a large cpu systems Vishal Chourasia
2022-10-17 14:19 ` Peter Zijlstra
2022-10-17 14:54   ` Greg Kroah-Hartman
2022-10-18 10:37     ` Vishal Chourasia
2022-10-18 11:04       ` Greg Kroah-Hartman
2022-10-18 11:04         ` Greg Kroah-Hartman
2022-10-26  6:37         ` Vishal Chourasia [this message]
2022-10-26  6:37           ` Vishal Chourasia
2022-10-26  7:02           ` Greg Kroah-Hartman
2022-10-26  7:02             ` Greg Kroah-Hartman
2022-10-26  9:10             ` Peter Zijlstra
2022-10-26  9:10               ` Peter Zijlstra
2022-11-08 10:00               ` Vishal Chourasia
2022-11-08 10:00                 ` Vishal Chourasia
2022-11-08 12:24                 ` Greg Kroah-Hartman
2022-11-08 12:24                   ` Greg Kroah-Hartman
2022-11-08 14:51                   ` Srikar Dronamraju
2022-11-08 14:51                     ` Srikar Dronamraju
2022-11-08 15:38                     ` Greg Kroah-Hartman
2022-11-08 15:38                       ` Greg Kroah-Hartman
2022-12-12 19:17                   ` Phil Auld
2022-12-12 19:17                     ` Phil Auld
2022-12-13  2:17                     ` kernel test robot
2022-12-13  2:17                       ` kernel test robot
2022-12-13  6:23                     ` Greg Kroah-Hartman
2022-12-13  6:23                       ` Greg Kroah-Hartman
2022-12-13 13:22                       ` Phil Auld
2022-12-13 13:22                         ` Phil Auld
2022-12-13 14:31                         ` Greg Kroah-Hartman
2022-12-13 14:31                           ` Greg Kroah-Hartman
2022-12-13 14:45                           ` Phil Auld
2022-12-13 14:45                             ` Phil Auld
2023-01-19 15:31                           ` Phil Auld
2023-01-19 15:31                             ` Phil Auld
2022-12-13 23:41                         ` Michael Ellerman
2022-12-13 23:41                           ` Michael Ellerman
2022-12-14  2:26                           ` Phil Auld
2022-12-14  2:26                             ` Phil Auld

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