[PATCH v2 1/2] Documentation: scheduler: fix outdated information on arch SD flags and sched_domain

[PATCH v2 1/2] Documentation: scheduler: fix outdated information on arch SD flags and sched_domain

[Barry Song]

This document seems to be out of date for many, many years. Even it has
misspelled from the first day.
ARCH_HASH_SCHED_TUNE should be ARCH_HAS_SCHED_TUNE
ARCH_HASH_SCHED_DOMAIN should be ARCH_HAS_SCHED_DOMAIN

Since v2.6.14, kernel completely deleted the relevant code and even
arch_init_sched_domains() was deleted.

Right now, kernel is asking architectures to call set_sched_topology() to
override the default sched domains.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Adrian Freund <adrian@freund.io>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
---
 -v2: refine the SD_ flags description with respect to Valentin's comment

 Documentation/scheduler/sched-domains.rst | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/Documentation/scheduler/sched-domains.rst b/Documentation/scheduler/sched-domains.rst
index 5c4b7f4f0062..55983b7e1098 100644
--- a/Documentation/scheduler/sched-domains.rst
+++ b/Documentation/scheduler/sched-domains.rst
@@ -65,19 +65,13 @@ of the SMP domain will span the entire machine, with each group having the
 cpumask of a node. Or, you could do multi-level NUMA or Opteron, for example,
 might have just one domain covering its one NUMA level.
 
-The implementor should read comments in include/linux/sched.h:
-struct sched_domain fields, SD_FLAG_*, SD_*_INIT to get an idea of
-the specifics and what to tune.
+The implementor should read comments in include/linux/sched/sd_flags.h:
+SD_* to get an idea of the specifics and what to tune for the SD flags
+of a sched_domain.
 
-Architectures may retain the regular override the default SD_*_INIT flags
-while using the generic domain builder in kernel/sched/core.c if they wish to
-retain the traditional SMT->SMP->NUMA topology (or some subset of that). This
-can be done by #define'ing ARCH_HASH_SCHED_TUNE.
-
-Alternatively, the architecture may completely override the generic domain
-builder by #define'ing ARCH_HASH_SCHED_DOMAIN, and exporting your
-arch_init_sched_domains function. This function will attach domains to all
-CPUs using cpu_attach_domain.
+Architectures may override the generic domain builder and the default SD flags
+for a given topology level by creating a sched_domain_topology_level array and
+calling set_sched_topology() with this array as the parameter.
 
 The sched-domains debugging infrastructure can be enabled by enabling
 CONFIG_SCHED_DEBUG. This enables an error checking parse of the sched domains
-- 
2.25.1

[PATCH v2 2/2] Documentation: scheduler: ask users to set sched_debug cmdline

[Barry Song]

From: Valentin Schneider <valentin.schneider@arm.com>

To print the schedule debug information, users need to set sched_debug
cmdline or enable it by sysfs entry.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Adrian Freund <adrian@freund.io>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
---
 Documentation/scheduler/sched-domains.rst | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/Documentation/scheduler/sched-domains.rst b/Documentation/scheduler/sched-domains.rst
index 55983b7e1098..8582fa5e9170 100644
--- a/Documentation/scheduler/sched-domains.rst
+++ b/Documentation/scheduler/sched-domains.rst
@@ -74,6 +74,8 @@ for a given topology level by creating a sched_domain_topology_level array and
 calling set_sched_topology() with this array as the parameter.
 
 The sched-domains debugging infrastructure can be enabled by enabling
-CONFIG_SCHED_DEBUG. This enables an error checking parse of the sched domains
-which should catch most possible errors (described above). It also prints out
-the domain structure in a visual format.
+CONFIG_SCHED_DEBUG and adding 'sched_debug' to your cmdline. If you forgot to
+tweak your cmdline, you can also flip the /sys/kernel/debug/sched_debug
+knob. This enables an error checking parse of the sched domains which should
+catch most possible errors (described above). It also prints out the domain
+structure in a visual format.
-- 
2.25.1

Re: [PATCH v2 2/2] Documentation: scheduler: ask users to set sched_debug cmdline

[Valentin Schneider]

On 12/11/20 22:31, Barry Song wrote:
> From: Valentin Schneider <valentin.schneider@arm.com>
>
> To print the schedule debug information, users need to set sched_debug
> cmdline or enable it by sysfs entry.
>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Adrian Freund <adrian@freund.io>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>

FYI, forging SoB, or any 'tag' other than Suggested-by / Reported-by is
frowned up. Now I do appreciate your effort to give me credit, but in this
case you should've used Suggested-by.

Moreso, this really is a trivial change and doesn't deserve a separate
patch, so I would say just squash that into patch 1, and add

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

to it :)

> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> ---
>  Documentation/scheduler/sched-domains.rst | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/scheduler/sched-domains.rst b/Documentation/scheduler/sched-domains.rst
> index 55983b7e1098..8582fa5e9170 100644
> --- a/Documentation/scheduler/sched-domains.rst
> +++ b/Documentation/scheduler/sched-domains.rst
> @@ -74,6 +74,8 @@ for a given topology level by creating a sched_domain_topology_level array and
>  calling set_sched_topology() with this array as the parameter.
>  
>  The sched-domains debugging infrastructure can be enabled by enabling
> -CONFIG_SCHED_DEBUG. This enables an error checking parse of the sched domains
> -which should catch most possible errors (described above). It also prints out
> -the domain structure in a visual format.
> +CONFIG_SCHED_DEBUG and adding 'sched_debug' to your cmdline. If you forgot to
> +tweak your cmdline, you can also flip the /sys/kernel/debug/sched_debug
> +knob. This enables an error checking parse of the sched domains which should
> +catch most possible errors (described above). It also prints out the domain
> +structure in a visual format.

RE: [PATCH v2 2/2] Documentation: scheduler: ask users to set sched_debug cmdline

[Song Bao Hua (Barry Song)]

> -----Original Message-----
> From: Valentin Schneider [mailto:valentin.schneider@arm.com]
> Sent: Saturday, November 14, 2020 12:34 AM
> To: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>
> Cc: corbet@lwn.net; linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org;
> Linuxarm <linuxarm@huawei.com>; Ingo Molnar <mingo@redhat.com>; Peter
> Zijlstra <peterz@infradead.org>; Mel Gorman <mgorman@suse.de>; Adrian
> Freund <adrian@freund.io>
> Subject: Re: [PATCH v2 2/2] Documentation: scheduler: ask users to set
> sched_debug cmdline
> 
> 
> On 12/11/20 22:31, Barry Song wrote:
> > From: Valentin Schneider <valentin.schneider@arm.com>
> >
> > To print the schedule debug information, users need to set sched_debug
> > cmdline or enable it by sysfs entry.
> >
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Mel Gorman <mgorman@suse.de>
> > Cc: Adrian Freund <adrian@freund.io>
> > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> 
> FYI, forging SoB, or any 'tag' other than Suggested-by / Reported-by is
> frowned up. Now I do appreciate your effort to give me credit, but in this
> case you should've used Suggested-by.

As this part is actually your code, so I put an --author=" Valentin ..." in
git commit so that git can show you are the author. Actually I was not
sure if SoB was proper when I made it. My intention was only telling
people the code was from you :-)

> 
> Moreso, this really is a trivial change and doesn't deserve a separate
> patch, so I would say just squash that into patch 1, and add
> 
> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> 
> to it :)

Cool, thanks.

> 
> > Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> > ---
> >  Documentation/scheduler/sched-domains.rst | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/scheduler/sched-domains.rst
> b/Documentation/scheduler/sched-domains.rst
> > index 55983b7e1098..8582fa5e9170 100644
> > --- a/Documentation/scheduler/sched-domains.rst
> > +++ b/Documentation/scheduler/sched-domains.rst
> > @@ -74,6 +74,8 @@ for a given topology level by creating a
> sched_domain_topology_level array and
> >  calling set_sched_topology() with this array as the parameter.
> >
> >  The sched-domains debugging infrastructure can be enabled by enabling
> > -CONFIG_SCHED_DEBUG. This enables an error checking parse of the sched
> domains
> > -which should catch most possible errors (described above). It also prints out
> > -the domain structure in a visual format.
> > +CONFIG_SCHED_DEBUG and adding 'sched_debug' to your cmdline. If you
> forgot to
> > +tweak your cmdline, you can also flip the /sys/kernel/debug/sched_debug
> > +knob. This enables an error checking parse of the sched domains which
> should
> > +catch most possible errors (described above). It also prints out the domain
> > +structure in a visual format.

Thanks
Barry