All of lore.kernel.org
 help / color / mirror / Atom feed
From: Juri Lelli <juri.lelli@gmail.com>
To: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Cc: quentin.perret@arm.com, sudeep.holla@arm.com,
	dietmar.eggemann@arm.com, gregkh@linuxfoundation.org,
	will.deacon@arm.com, catalin.marinas@arm.com,
	morten.rasmussen@arm.com, linux-arm-kernel@lists.infradead.org,
	jeremy.linton@arm.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] arch_topology: Make cpu_capacity sysfs node as ready-only
Date: Thu, 7 Mar 2019 08:28:56 +0100	[thread overview]
Message-ID: <20190307072856.GC29753@localhost.localdomain> (raw)
In-Reply-To: <1551886073-16217-1-git-send-email-clingutla@codeaurora.org>

Hi,

On 06/03/19 20:57, Lingutla Chandrasekhar wrote:
> If user updates any cpu's cpu_capacity, then the new value is going to
> be applied to all its online sibling cpus. But this need not to be correct
> always, as sibling cpus (in ARM, same micro architecture cpus) would have
> different cpu_capacity with different performance characteristics.
> So updating the user supplied cpu_capacity to all cpu siblings
> is not correct.
> 
> And another problem is, current code assumes that 'all cpus in a cluster
> or with same package_id (core_siblings), would have same cpu_capacity'.
> But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
> cpu topology sibling masks")', when a cpu hotplugged out, the cpu
> information gets cleared in its sibling cpus. So user supplied
> cpu_capacity would be applied to only online sibling cpus at the time.
> After that, if any cpu hot plugged in, it would have different cpu_capacity
> than its siblings, which breaks the above assumption.
> 
> So instead of mucking around the core sibling mask for user supplied
> value, use device-tree to set cpu capacity. And make the cpu_capacity
> node as read-only to know the assymetry between cpus in the system.
> 
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
> ---
>  drivers/base/arch_topology.c | 33 +--------------------------------
>  1 file changed, 1 insertion(+), 32 deletions(-)
> 
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index edfcf8d..d455897 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -7,7 +7,6 @@
>   */
>  
>  #include <linux/acpi.h>
> -#include <linux/arch_topology.h>
>  #include <linux/cpu.h>
>  #include <linux/cpufreq.h>
>  #include <linux/device.h>
> @@ -51,37 +50,7 @@ static ssize_t cpu_capacity_show(struct device *dev,
>  static void update_topology_flags_workfn(struct work_struct *work);
>  static DECLARE_WORK(update_topology_flags_work, update_topology_flags_workfn);
>  
> -static ssize_t cpu_capacity_store(struct device *dev,
> -				  struct device_attribute *attr,
> -				  const char *buf,
> -				  size_t count)
> -{
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> -	int this_cpu = cpu->dev.id;
> -	int i;
> -	unsigned long new_capacity;
> -	ssize_t ret;
> -
> -	if (!count)
> -		return 0;
> -
> -	ret = kstrtoul(buf, 0, &new_capacity);
> -	if (ret)
> -		return ret;
> -	if (new_capacity > SCHED_CAPACITY_SCALE)
> -		return -EINVAL;
> -
> -	mutex_lock(&cpu_scale_mutex);
> -	for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
> -		topology_set_cpu_scale(i, new_capacity);
> -	mutex_unlock(&cpu_scale_mutex);
> -
> -	schedule_work(&update_topology_flags_work);
> -
> -	return count;
> -}
> -
> -static DEVICE_ATTR_RW(cpu_capacity);
> +static DEVICE_ATTR_RO(cpu_capacity);

There are cases in which this needs to be RW, as recently discussed
https://lore.kernel.org/lkml/20181123135807.GA14964@e107155-lin/

IMHO, if the core_sibling assumption doesn't work in all cases, one
should be looking into fixing it, rather than making this RO.

Best,

- Juri

WARNING: multiple messages have this Message-ID (diff)
From: Juri Lelli <juri.lelli@gmail.com>
To: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Cc: catalin.marinas@arm.com, sudeep.holla@arm.com,
	will.deacon@arm.com, linux-kernel@vger.kernel.org,
	jeremy.linton@arm.com, morten.rasmussen@arm.com,
	quentin.perret@arm.com, gregkh@linuxfoundation.org,
	dietmar.eggemann@arm.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v1] arch_topology: Make cpu_capacity sysfs node as ready-only
Date: Thu, 7 Mar 2019 08:28:56 +0100	[thread overview]
Message-ID: <20190307072856.GC29753@localhost.localdomain> (raw)
In-Reply-To: <1551886073-16217-1-git-send-email-clingutla@codeaurora.org>

Hi,

On 06/03/19 20:57, Lingutla Chandrasekhar wrote:
> If user updates any cpu's cpu_capacity, then the new value is going to
> be applied to all its online sibling cpus. But this need not to be correct
> always, as sibling cpus (in ARM, same micro architecture cpus) would have
> different cpu_capacity with different performance characteristics.
> So updating the user supplied cpu_capacity to all cpu siblings
> is not correct.
> 
> And another problem is, current code assumes that 'all cpus in a cluster
> or with same package_id (core_siblings), would have same cpu_capacity'.
> But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
> cpu topology sibling masks")', when a cpu hotplugged out, the cpu
> information gets cleared in its sibling cpus. So user supplied
> cpu_capacity would be applied to only online sibling cpus at the time.
> After that, if any cpu hot plugged in, it would have different cpu_capacity
> than its siblings, which breaks the above assumption.
> 
> So instead of mucking around the core sibling mask for user supplied
> value, use device-tree to set cpu capacity. And make the cpu_capacity
> node as read-only to know the assymetry between cpus in the system.
> 
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
> ---
>  drivers/base/arch_topology.c | 33 +--------------------------------
>  1 file changed, 1 insertion(+), 32 deletions(-)
> 
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index edfcf8d..d455897 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -7,7 +7,6 @@
>   */
>  
>  #include <linux/acpi.h>
> -#include <linux/arch_topology.h>
>  #include <linux/cpu.h>
>  #include <linux/cpufreq.h>
>  #include <linux/device.h>
> @@ -51,37 +50,7 @@ static ssize_t cpu_capacity_show(struct device *dev,
>  static void update_topology_flags_workfn(struct work_struct *work);
>  static DECLARE_WORK(update_topology_flags_work, update_topology_flags_workfn);
>  
> -static ssize_t cpu_capacity_store(struct device *dev,
> -				  struct device_attribute *attr,
> -				  const char *buf,
> -				  size_t count)
> -{
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> -	int this_cpu = cpu->dev.id;
> -	int i;
> -	unsigned long new_capacity;
> -	ssize_t ret;
> -
> -	if (!count)
> -		return 0;
> -
> -	ret = kstrtoul(buf, 0, &new_capacity);
> -	if (ret)
> -		return ret;
> -	if (new_capacity > SCHED_CAPACITY_SCALE)
> -		return -EINVAL;
> -
> -	mutex_lock(&cpu_scale_mutex);
> -	for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
> -		topology_set_cpu_scale(i, new_capacity);
> -	mutex_unlock(&cpu_scale_mutex);
> -
> -	schedule_work(&update_topology_flags_work);
> -
> -	return count;
> -}
> -
> -static DEVICE_ATTR_RW(cpu_capacity);
> +static DEVICE_ATTR_RO(cpu_capacity);

There are cases in which this needs to be RW, as recently discussed
https://lore.kernel.org/lkml/20181123135807.GA14964@e107155-lin/

IMHO, if the core_sibling assumption doesn't work in all cases, one
should be looking into fixing it, rather than making this RO.

Best,

- Juri

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2019-03-07  7:29 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-28 11:53 [PATCH] arch_topology: Update user supplied capacity to possible cpus in cluster Lingutla Chandrasekhar
2019-02-28 12:19 ` Sudeep Holla
2019-02-28 14:38   ` Chandra Sekhar Lingutla
2019-02-28 15:25     ` Sudeep Holla
2019-03-02 13:30       ` Chandra Sekhar Lingutla
2019-03-04 18:21         ` Sudeep Holla
2019-03-05  9:23           ` Quentin Perret
2019-03-05 11:13             ` Sudeep Holla
2019-03-05 11:29               ` Quentin Perret
2019-03-05 11:36                 ` Sudeep Holla
2019-03-05 15:53                   ` Chandra Sekhar Lingutla
2019-03-05 16:12                     ` Quentin Perret
2019-03-05 16:54                     ` Sudeep Holla
2019-03-06 15:22                       ` Morten Rasmussen
2019-03-06 15:27                         ` [PATCH v1] arch_topology: Make cpu_capacity sysfs node as ready-only Lingutla Chandrasekhar
2019-03-06 15:27                           ` Lingutla Chandrasekhar
2019-03-07  7:28                           ` Juri Lelli [this message]
2019-03-07  7:28                             ` Juri Lelli
2019-03-07  9:31                             ` Quentin Perret
2019-03-07  9:31                               ` Quentin Perret
2019-03-07  9:57                               ` Juri Lelli
2019-03-07  9:57                                 ` Juri Lelli
2019-03-07 12:14                                 ` Quentin Perret
2019-03-07 12:14                                   ` Quentin Perret
2019-03-07 15:04                                   ` Sudeep Holla
2019-03-07 15:04                                     ` Sudeep Holla
2019-03-07 15:19                           ` Sudeep Holla
2019-03-07 15:19                             ` Sudeep Holla
2019-03-08 11:45                           ` Dietmar Eggemann
2019-03-08 11:45                             ` Dietmar Eggemann
2019-03-08 12:38                             ` [PATCH v2] " Lingutla Chandrasekhar
2019-03-08 12:38                               ` Lingutla Chandrasekhar
2019-03-27 10:56                               ` Quentin Perret
2019-03-27 10:56                                 ` Quentin Perret
2019-03-06  9:48                 ` [PATCH] arch_topology: Update user supplied capacity to possible cpus in cluster Dietmar Eggemann

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190307072856.GC29753@localhost.localdomain \
    --to=juri.lelli@gmail.com \
    --cc=catalin.marinas@arm.com \
    --cc=clingutla@codeaurora.org \
    --cc=dietmar.eggemann@arm.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=jeremy.linton@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=morten.rasmussen@arm.com \
    --cc=quentin.perret@arm.com \
    --cc=sudeep.holla@arm.com \
    --cc=will.deacon@arm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.