Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

[Alejandro Colomar]

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Hi Branden,

On 2/15/23 02:20, G. Branden Robinson wrote:
> [CC list violently trimmed; for those who remain, this is mostly man
> page style issues]

Ironically, you trimmed linux-man@  :D

> 
> At 2023-02-14T23:29:37+0100, Alejandro Colomar wrote:
>> On 2/14/23 20:54, Mathieu Desnoyers wrote:
>>> +per-thread data structure shared between kernel and user-space.
>>
>> This last 'user-space' is not adjectivated, so it should go without
>> a hyphen, according to common English rules.
> 
> +1
> 
> Also I like your coinage.  "Adjectivated yeast" is reflexive and
> tautological!

:D

I didn't even think about it.  "adjetivado" is an actual word in Spanish,
so I just guessed that it would exist in English.  But yes, it's a nice
word for this case :)

> 
>>> +.RB ( "struct rseq" )
>>
>> We format types in italics, so this should be '.RI'.
> 
> +1
> 
>>> +Only one
>>> +.BR rseq ()
>>> +ABI can be registered per thread, so user-space libraries and
>>> +applications must follow a user-space ABI defining how to share this
>>> +resource.
>>
>> Please use semantic newlines.  See man-pages(7):
>>
>>    Use semantic newlines
>>        In  the source of a manual page, new sentences should be started on new
>>        lines, long sentences should be split into lines at clause breaks (com‐
>>        mas, semicolons, colons, and so on), and long clauses should  be  split
>>        at  phrase  boundaries.   This convention, sometimes known as "semantic
>>        newlines", makes it easier to see the effect of  patches,  which  often
>>        operate at the level of individual sentences, clauses, or phrases.
> 
> I think I've said this before, but, strictly, commas in particular can
> separate things that are not clauses.  Clauses have subjects and
> predicates.
> 
> Might it be better to say simply:
> 
>   Start each sentence on a new line.  Split long sentences where
>   punctuated by commas, semicolons, and colons.
> 
> With this there is not even any need to discuss "phrase boundaries".

I still disagree with that;
punctuation is not enough
(see below).

> 
>> In the above lines, that would mean breaking after the comma,
>> and not leaving resource in a line of its own.
> 
> The latter is inevitably going to happen from time to time simply due to
> sentence length and structure and the line length used by one's text
> editor.

That's if you only break at sentence and clause boundaries,
and then adjust at 80 columns...

>  I don't think an "orphan word" (what typographers call this) is
> symptomatic of anything in *roff source when filling is enabled.

but if you also break at phrase boundaries
(when/where convenient)
you'll find that you get rid of those "orphan words",
because you'll never have to adjust at 80 columns
(or rather,
you'll try to find a way to break it
that also happens to be a phrase boundary
because breaking at phrase boundaries is _better_
than breaking at random points which may happen to be
in the middle of a compound noun).

> 
>>> +The ABI defining how to share this resource between applications and
>>> +libraries is defined by the C library.
>>> +Allocation of the per-thread
>>> +.BR rseq ()
>>> +ABI and its registration to the kernel is handled by glibc since version
>>> +2.35.
>>> +.PP
>>> +The
>>> +.BR rseq ()
>>> +ABI per-thread data structure contains a
>>> +.I rseq_cs
>>> +field which points to the currently executing critical section.
>>
>> currently-executing should probably use a hyphen
>> (if I understood the line correctly).
> 
> This is not the case, according to some style authorities.  Dave Kemper
> convinced me of this on the groff list.
> 
> Here is one resource.
> 
> https://www.editorgroup.com/blog/to-hyphenate-or-not-to-hyphenate/

Hmm, interesting.  I didn't think about it, but it makes sense
to not hyphenate here.

> 
>> See an interesting discussion in the groff@ mailing list:
>> <https://lists.gnu.org/archive/html/groff/2022-10/msg00015.html>
> 
> That's not _squarely_ on point, as none of "block", "device", or "based"
> is an adverb.  "Currently" is.

You're right.

> 
>>> +For each thread, a single rseq critical section can run at any given
>>> +point.
>>> +Each critical section need to be implemented in assembly.
>>
>> needs?
> 
> +1
> 
>>> +.TP
>>> +.B Structure alignment
>>
>> Let's remove the bold here.  It's not necessary for marking a constant
>> or something that needs bold.  And the indentation is already making
>> it stand out, so bold is a bit too much aggressive to the reader.
> 
> I agree; if it wouldn't be styled in running text, it doesn't need
> styling as a paragraph tag; it already stands out by dint of its
> placement as a tag.
> 
>>> +Its value should always be confirmed by reading the cpu_id field before
>>
>> cpu_id should be formatted (.I).
> 
> +1
> 
>>> +user-space performs any side-effect
>>> +(e.g. storing to memory).
>>> +.IP
>>> +This field is always guaranteed to hold a valid CPU number in the range
>>> +[ 0 ..  nr_possible_cpus - 1 ].
>>
>> Please use interval notation:
>> 	[0, nr_possible_cpus)
>> or
>> 	[0, nr_possible_cpus - 1]
>> whichever looks better to you.
>>
>> We did some consistency fix recently:
>> <https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=147a60d792a5db8f3cb93ea16eefb73e16c1fb91>
>>
>> Also, do we have a more standard way of saying nr_possible_cpus?
>> Should we say nproc?
> 
> Apropos of a separate discussion we had weeks ago, Alex, I remembered
> where I saw "nitems" as a variable name.
> 
> _UNIX Programming_, second edition, by Kernighan and Ritchie!
> 
> https://wolfram.schneider.org/bsd/7thEdManVol2/uprog/uprog.pdf
> 
> Plop _that_ down on the desk of the person who claimed it was a stupid
> variable name that no good programmer would ever use.

ROFL.  I'm bookmarking this!

> 
> (I think appeals to authority are just fine as long as one is being
> mean.  ;-P

Indeed ;-P

>  And as regards variable naming, Kernighan is a _legitimate_
> authority: a subject matter expert with multiple well-regarded books on
> coding style to his credit.  Ritchie's strengths were more esoteric,
> enough that he put up specimens of his own youthful hubris as, I think,
> an effort to discourage his many admirers from copying his mistakes as
> slavishly as his successes[1]--apart from their humor value.)
> 
>> Branden, IIRC, this seems to be the reason why I didn't want .RS for
>> indenting code examples.  It doesn't fit nicely right after TP.
>>
>> Why is there a blank line?  I'm not even sure that's reasonable.  Is
>> it a (minor) bug in man(7)?  (FWIW, mandoc(1) is consistent with
>> groff(1).)
> 
> Right, I'll take this up in the separate thread you started for it on
> the groff list.

Sure.

> 
> Regards,
> Branden
> 
> [1] https://www.bell-labs.com/usr/dmr/www/odd.html
> 
>     See particularly "Comments I do feel guilty about".

Yep, that page is always funny :)

Cheers,

Alex


-- 
<http://www.alejandro-colomar.es/>
GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5

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Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

[G. Branden Robinson]

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At 2023-02-15T02:52:03+0100, Alejandro Colomar wrote:
> On 2/15/23 02:20, G. Branden Robinson wrote:
> > [CC list violently trimmed; for those who remain, this is mostly man
> > page style issues]
> 
> Ironically, you trimmed linux-man@  :D

I didn't!  It wasn't present in the mail to which I repled.

This did puzzle me.  I guess it was an oversight.  You might want to
re-send that message of yours, and/or Mathieu's, if it lacked it too.

Or maybe it doesn't matter because lore.kernel.org finds all.  I just
used it to track down an exchange between Michael Kerrisk and me that
GMail refused to find even though it was in my inbox.  It showed me only
one thread, didn't highlight the specific message that it thought
matched, and showed me the _wrong_ thread on top of everything else.
The word "constraint" was in the thread I wanted, not in the one I
didn't, and even when I quoted it I was served up an incorrect match.

Clearly their AI efforts are going swimmingly.

Regards,
Branden

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Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

[Alejandro Colomar]

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Hi Branden,

On 2/15/23 03:21, G. Branden Robinson wrote:
> At 2023-02-15T02:52:03+0100, Alejandro Colomar wrote:
>> On 2/15/23 02:20, G. Branden Robinson wrote:
>>> [CC list violently trimmed; for those who remain, this is mostly man
>>> page style issues]
>>
>> Ironically, you trimmed linux-man@  :D
> 
> I didn't!  It wasn't present in the mail to which I repled.

Hmm, you're right, Mathieu didn't CC linux-man@.  I guessed somewhere
in that big list it would be there, but it wasn't.  Thanks for CCing it.

> 
> This did puzzle me.  I guess it was an oversight.  You might want to
> re-send that message of yours, and/or Mathieu's, if it lacked it too.
> 
> Or maybe it doesn't matter because lore.kernel.org finds all.  I just
> used it to track down an exchange between Michael Kerrisk and me that
> GMail refused to find even though it was in my inbox.  It showed me only
> one thread, didn't highlight the specific message that it thought
> matched, and showed me the _wrong_ thread on top of everything else.
> The word "constraint" was in the thread I wanted, not in the one I
> didn't, and even when I quoted it I was served up an incorrect match.

Which reminds me that I hate searching in the groff@ archives.  It's not
because of the search engine, but because of the thread view.  You are
artificially restricted to a given month, and you can't see entire threads
in the search engine.  Is there anything similar to lore for groff@?
Other GNU projects can now be searched at <https://inbox.sourceware.org/>
such as <https://inbox.sourceware.org/libc-alpha/>, but groff@ isn't there
:(

Cheers,

Alex

> 
> Clearly their AI efforts are going swimmingly.> 
> Regards,
> Branden

-- 
<http://www.alejandro-colomar.es/>
GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5

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Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

[Mathieu Desnoyers]

On 2023-02-14 22:07, Alejandro Colomar wrote:
> Hi Branden,
> 
> On 2/15/23 03:21, G. Branden Robinson wrote:
>> At 2023-02-15T02:52:03+0100, Alejandro Colomar wrote:
>>> On 2/15/23 02:20, G. Branden Robinson wrote:
>>>> [CC list violently trimmed; for those who remain, this is mostly man
>>>> page style issues]
>>>
>>> Ironically, you trimmed linux-man@  :D
>>
>> I didn't!  It wasn't present in the mail to which I repled.
> 
> Hmm, you're right, Mathieu didn't CC linux-man@.  I guessed somewhere
> in that big list it would be there, but it wasn't.  Thanks for CCing it.
> 
>>
>> This did puzzle me.  I guess it was an oversight.  You might want to
>> re-send that message of yours, and/or Mathieu's, if it lacked it too.

My bad. The list I used was from a script I last updated when I was 
trying to get Michael's attention a few years ago. I've trimmed it and 
included linux-man@.

I will use that new email list for my next post taking your comments 
into account.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

[Mathieu Desnoyers]

On 2023-02-14 20:20, G. Branden Robinson wrote:
> [CC list violently trimmed; for those who remain, this is mostly man
> page style issues]

[ Gently added linux-man to CC list. ;-) ]

> 
> At 2023-02-14T23:29:37+0100, Alejandro Colomar wrote:
>> On 2/14/23 20:54, Mathieu Desnoyers wrote:
>>> +per-thread data structure shared between kernel and user-space.
>>
>> This last 'user-space' is not adjectivated, so it should go without
>> a hyphen, according to common English rules.
> 
> +1

done


> 
> Also I like your coinage.  "Adjectivated yeast" is reflexive and
> tautological!
> 
>>> +.RB ( "struct rseq" )
>>
>> We format types in italics, so this should be '.RI'.
> 
> +1

OK, so it's italics for both types and arguments.

I will replace all the bold markers for "struct rseq" and "struct 
rseq_cs" to italic in the description (but not in the synopsis section 
and not in the code snippets).

> 
>>> +Only one
>>> +.BR rseq ()
>>> +ABI can be registered per thread, so user-space libraries and
>>> +applications must follow a user-space ABI defining how to share this
>>> +resource.
>>
>> Please use semantic newlines.  See man-pages(7):
>>
>>     Use semantic newlines
>>         In  the source of a manual page, new sentences should be started on new
>>         lines, long sentences should be split into lines at clause breaks (com‐
>>         mas, semicolons, colons, and so on), and long clauses should  be  split
>>         at  phrase  boundaries.   This convention, sometimes known as "semantic
>>         newlines", makes it easier to see the effect of  patches,  which  often
>>         operate at the level of individual sentences, clauses, or phrases.
> 
> I think I've said this before, but, strictly, commas in particular can
> separate things that are not clauses.  Clauses have subjects and
> predicates.
> 
> Might it be better to say simply:
> 
>    Start each sentence on a new line.  Split long sentences where
>    punctuated by commas, semicolons, and colons.
> 
> With this there is not even any need to discuss "phrase boundaries".
> 

I've modified to:

Only one
.BR rseq ()
ABI can be registered per thread,
so user-space libraries and applications must follow a user-space ABI
defining how to share this resource.

Hopefully that's correct.


>> In the above lines, that would mean breaking after the comma,
>> and not leaving resource in a line of its own.
> 
> The latter is inevitably going to happen from time to time simply due to
> sentence length and structure and the line length used by one's text
> editor.  I don't think an "orphan word" (what typographers call this) is
> symptomatic of anything in *roff source when filling is enabled.
> 
>>> +The ABI defining how to share this resource between applications and
>>> +libraries is defined by the C library.
>>> +Allocation of the per-thread
>>> +.BR rseq ()
>>> +ABI and its registration to the kernel is handled by glibc since version
>>> +2.35.
>>> +.PP
>>> +The
>>> +.BR rseq ()
>>> +ABI per-thread data structure contains a
>>> +.I rseq_cs
>>> +field which points to the currently executing critical section.
>>
>> currently-executing should probably use a hyphen
>> (if I understood the line correctly).
> 
> This is not the case, according to some style authorities.  Dave Kemper
> convinced me of this on the groff list.
> 
> Here is one resource.
> 
> https://www.editorgroup.com/blog/to-hyphenate-or-not-to-hyphenate/
> 
>> See an interesting discussion in the groff@ mailing list:
>> <https://lists.gnu.org/archive/html/groff/2022-10/msg00015.html>
> 
> That's not _squarely_ on point, as none of "block", "device", or "based"
> is an adverb.  "Currently" is.

Leaving unchanged based on this discussion.

> 
>>> +For each thread, a single rseq critical section can run at any given
>>> +point.
>>> +Each critical section need to be implemented in assembly.
>>
>> needs?
> 
> +1

done.

> 
>>> +.TP
>>> +.B Structure alignment
>>
>> Let's remove the bold here.  It's not necessary for marking a constant
>> or something that needs bold.  And the indentation is already making
>> it stand out, so bold is a bit too much aggressive to the reader.
> 
> I agree; if it wouldn't be styled in running text, it doesn't need
> styling as a paragraph tag; it already stands out by dint of its
> placement as a tag.
> 
>>> +Its value should always be confirmed by reading the cpu_id field before
>>
>> cpu_id should be formatted (.I).
> 
> +1

done

> 
>>> +user-space performs any side-effect
>>> +(e.g. storing to memory).
>>> +.IP
>>> +This field is always guaranteed to hold a valid CPU number in the range
>>> +[ 0 ..  nr_possible_cpus - 1 ].
>>
>> Please use interval notation:
>> 	[0, nr_possible_cpus)
>> or
>> 	[0, nr_possible_cpus - 1]
>> whichever looks better to you.
>>
>> We did some consistency fix recently:
>> <https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=147a60d792a5db8f3cb93ea16eefb73e16c1fb91>
>>
>> Also, do we have a more standard way of saying nr_possible_cpus?
>> Should we say nproc?

nproc(1) means:

        Print  the number of processing units available to the current
        process, which may be less than the number of online processors

Which is the number of cpus currently available (AFAIU the result of the
cpuset and sched affinity).

What I really mean here is the maximum value for possible cpus which can 
be hotplugged into the system. So it's not the maximum number of 
possible CPUs per se, but rather the maximum enabled bit in the possible 
CPUs mask.

Note that we could express this differently as well: rather than saying 
that it guarantees a value in the range [0, nr_possible_cpus - 1], we 
could say that the values are guaranteed to be part of the possible cpus 
mask, which would actually more accurate in case the possible cpus mask 
has a hole (it tends to happen with things like lxc containers nowadays).

Do you agree that we should favor expressing this in terms of belonging 
to the possible cpumask set rather than a range starting from 0 ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

[Mathieu Desnoyers]

On 2023-02-15 12:09, Mathieu Desnoyers wrote:
> On 2023-02-14 20:20, G. Branden Robinson wrote:
[...]
>>
>>>> +user-space performs any side-effect
>>>> +(e.g. storing to memory).
>>>> +.IP
>>>> +This field is always guaranteed to hold a valid CPU number in the 
>>>> range
>>>> +[ 0 ..  nr_possible_cpus - 1 ].
>>>
>>> Please use interval notation:
>>>     [0, nr_possible_cpus)
>>> or
>>>     [0, nr_possible_cpus - 1]
>>> whichever looks better to you.
>>>
>>> We did some consistency fix recently:
>>> <https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=147a60d792a5db8f3cb93ea16eefb73e16c1fb91>
>>>
>>> Also, do we have a more standard way of saying nr_possible_cpus?
>>> Should we say nproc?
> 
> nproc(1) means:
> 
>         Print  the number of processing units available to the current
>         process, which may be less than the number of online processors
> 
> Which is the number of cpus currently available (AFAIU the result of the
> cpuset and sched affinity).
> 
> What I really mean here is the maximum value for possible cpus which can 
> be hotplugged into the system. So it's not the maximum number of 
> possible CPUs per se, but rather the maximum enabled bit in the possible 
> CPUs mask.
> 
> Note that we could express this differently as well: rather than saying 
> that it guarantees a value in the range [0, nr_possible_cpus - 1], we 
> could say that the values are guaranteed to be part of the possible cpus 
> mask, which would actually more accurate in case the possible cpus mask 
> has a hole (it tends to happen with things like lxc containers nowadays).
> 
> Do you agree that we should favor expressing this in terms of belonging 
> to the possible cpumask set rather than a range starting from 0 ?

Actually, the field may contain the value 0 even if 0 is not part of the 
possible cpumask. So forget what I just said about being guaranteed to 
be part of the possible cpus mask.

Thoughts ?

Thanks,

Mathieu

> 
> Thanks,
> 
> Mathieu
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

[Alejandro Colomar]

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Hi Mathieu,

On 2/15/23 18:09, Mathieu Desnoyers wrote:
> On 2023-02-14 20:20, G. Branden Robinson wrote:
>> [CC list violently trimmed; for those who remain, this is mostly man
>> page style issues]
> 
> [ Gently added linux-man to CC list. ;-) ]

:-)

> 
>>
>> At 2023-02-14T23:29:37+0100, Alejandro Colomar wrote:
>>> On 2/14/23 20:54, Mathieu Desnoyers wrote:
>>>> +per-thread data structure shared between kernel and user-space.
>>>
>>> This last 'user-space' is not adjectivated, so it should go without
>>> a hyphen, according to common English rules.
>>
>> +1
> 
> done
> 
> 
>>
>> Also I like your coinage.  "Adjectivated yeast" is reflexive and
>> tautological!
>>
>>>> +.RB ( "struct rseq" )
>>>
>>> We format types in italics, so this should be '.RI'.
>>
>> +1
> 
> OK, so it's italics for both types and arguments.
> 
> I will replace all the bold markers for "struct rseq" and "struct 
> rseq_cs" to italic in the description (but not in the synopsis section 
> and not in the code snippets).
> 
>>
>>>> +Only one
>>>> +.BR rseq ()
>>>> +ABI can be registered per thread, so user-space libraries and
>>>> +applications must follow a user-space ABI defining how to share this
>>>> +resource.
>>>
>>> Please use semantic newlines.  See man-pages(7):
>>>
>>>     Use semantic newlines
>>>         In  the source of a manual page, new sentences should be started on new
>>>         lines, long sentences should be split into lines at clause breaks (com‐
>>>         mas, semicolons, colons, and so on), and long clauses should  be  split
>>>         at  phrase  boundaries.   This convention, sometimes known as "semantic
>>>         newlines", makes it easier to see the effect of  patches,  which  often
>>>         operate at the level of individual sentences, clauses, or phrases.
>>
>> I think I've said this before, but, strictly, commas in particular can
>> separate things that are not clauses.  Clauses have subjects and
>> predicates.
>>
>> Might it be better to say simply:
>>
>>    Start each sentence on a new line.  Split long sentences where
>>    punctuated by commas, semicolons, and colons.
>>
>> With this there is not even any need to discuss "phrase boundaries".
>>
> 
> I've modified to:
> 
> Only one
> .BR rseq ()
> ABI can be registered per thread,
> so user-space libraries and applications must follow a user-space ABI
> defining how to share this resource.
> 
> Hopefully that's correct.

Yes, that's good.

> 
> 
>>> In the above lines, that would mean breaking after the comma,
>>> and not leaving resource in a line of its own.
>>
>> The latter is inevitably going to happen from time to time simply due to
>> sentence length and structure and the line length used by one's text
>> editor.  I don't think an "orphan word" (what typographers call this) is
>> symptomatic of anything in *roff source when filling is enabled.
>>
>>>> +The ABI defining how to share this resource between applications and
>>>> +libraries is defined by the C library.
>>>> +Allocation of the per-thread
>>>> +.BR rseq ()
>>>> +ABI and its registration to the kernel is handled by glibc since version
>>>> +2.35.
>>>> +.PP
>>>> +The
>>>> +.BR rseq ()
>>>> +ABI per-thread data structure contains a
>>>> +.I rseq_cs
>>>> +field which points to the currently executing critical section.
>>>
>>> currently-executing should probably use a hyphen
>>> (if I understood the line correctly).
>>
>> This is not the case, according to some style authorities.  Dave Kemper
>> convinced me of this on the groff list.
>>
>> Here is one resource.
>>
>> https://www.editorgroup.com/blog/to-hyphenate-or-not-to-hyphenate/
>>
>>> See an interesting discussion in the groff@ mailing list:
>>> <https://lists.gnu.org/archive/html/groff/2022-10/msg00015.html>
>>
>> That's not _squarely_ on point, as none of "block", "device", or "based"
>> is an adverb.  "Currently" is.
> 
> Leaving unchanged based on this discussion.
> 
>>
>>>> +For each thread, a single rseq critical section can run at any given
>>>> +point.
>>>> +Each critical section need to be implemented in assembly.
>>>
>>> needs?
>>
>> +1
> 
> done.
> 
>>
>>>> +.TP
>>>> +.B Structure alignment
>>>
>>> Let's remove the bold here.  It's not necessary for marking a constant
>>> or something that needs bold.  And the indentation is already making
>>> it stand out, so bold is a bit too much aggressive to the reader.
>>
>> I agree; if it wouldn't be styled in running text, it doesn't need
>> styling as a paragraph tag; it already stands out by dint of its
>> placement as a tag.
>>
>>>> +Its value should always be confirmed by reading the cpu_id field before
>>>
>>> cpu_id should be formatted (.I).
>>
>> +1
> 
> done
> 
>>
>>>> +user-space performs any side-effect
>>>> +(e.g. storing to memory).
>>>> +.IP
>>>> +This field is always guaranteed to hold a valid CPU number in the range
>>>> +[ 0 ..  nr_possible_cpus - 1 ].
>>>
>>> Please use interval notation:
>>> 	[0, nr_possible_cpus)
>>> or
>>> 	[0, nr_possible_cpus - 1]
>>> whichever looks better to you.
>>>
>>> We did some consistency fix recently:
>>> <https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=147a60d792a5db8f3cb93ea16eefb73e16c1fb91>
>>>
>>> Also, do we have a more standard way of saying nr_possible_cpus?
>>> Should we say nproc?
> 
> nproc(1) means:
> 
>         Print  the number of processing units available to the current
>         process, which may be less than the number of online processors
> 
> Which is the number of cpus currently available (AFAIU the result of the
> cpuset and sched affinity).
> 
> What I really mean here is the maximum value for possible cpus which can 
> be hotplugged into the system. So it's not the maximum number of 
> possible CPUs per se, but rather the maximum enabled bit in the possible 
> CPUs mask.
> 
> Note that we could express this differently as well: rather than saying 
> that it guarantees a value in the range [0, nr_possible_cpus - 1], we 
> could say that the values are guaranteed to be part of the possible cpus 
> mask, which would actually more accurate in case the possible cpus mask 
> has a hole (it tends to happen with things like lxc containers nowadays).
> 
> Do you agree that we should favor expressing this in terms of belonging 
> to the possible cpumask set rather than a range starting from 0 ?

On 2/15/23 18:12, Mathieu Desnoyers wrote:
> Actually, the field may contain the value 0 even if 0 is not part of the 
> possible cpumask. So forget what I just said about being guaranteed to 
> be part of the possible cpus mask.
> 
> Thoughts ?
> 
> Thanks,
> 
> Mathieu

I don't have a full understanding, so I will trust you for deciding what is
best.  I'll try to understand it, but my kernel knowledge is rather limited :)

I suggest writing a detailed description, instead of (or complementary to it)
just using a range, since readers might wonder as I did, what nr_possible_cpus
is (it's not really described anywhere so far).  With a worded description,
we can later improve it if we find it not clear enough, but should be enough
for an initial page.

Thanks!

Alex

> 
> Thanks,
> 
> Mathieu
> 

-- 
<http://www.alejandro-colomar.es/>
GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5

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Re: [PATCH 1/1] rseq.2: New man page for the rseq(2) API

[Mathieu Desnoyers]

On 2023-02-15 12:16, Alejandro Colomar wrote:
[...]
>>>
>>>>> +user-space performs any side-effect
>>>>> +(e.g. storing to memory).
>>>>> +.IP
>>>>> +This field is always guaranteed to hold a valid CPU number in the range
>>>>> +[ 0 ..  nr_possible_cpus - 1 ].
>>>>
>>>> Please use interval notation:
>>>> 	[0, nr_possible_cpus)
>>>> or
>>>> 	[0, nr_possible_cpus - 1]
>>>> whichever looks better to you.
>>>>
>>>> We did some consistency fix recently:
>>>> <https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=147a60d792a5db8f3cb93ea16eefb73e16c1fb91>
>>>>
>>>> Also, do we have a more standard way of saying nr_possible_cpus?
>>>> Should we say nproc?
>>
>> nproc(1) means:
>>
>>          Print  the number of processing units available to the current
>>          process, which may be less than the number of online processors
>>
>> Which is the number of cpus currently available (AFAIU the result of the
>> cpuset and sched affinity).
>>
>> What I really mean here is the maximum value for possible cpus which can
>> be hotplugged into the system. So it's not the maximum number of
>> possible CPUs per se, but rather the maximum enabled bit in the possible
>> CPUs mask.
>>
>> Note that we could express this differently as well: rather than saying
>> that it guarantees a value in the range [0, nr_possible_cpus - 1], we
>> could say that the values are guaranteed to be part of the possible cpus
>> mask, which would actually more accurate in case the possible cpus mask
>> has a hole (it tends to happen with things like lxc containers nowadays).
>>
>> Do you agree that we should favor expressing this in terms of belonging
>> to the possible cpumask set rather than a range starting from 0 ?
> 
> On 2/15/23 18:12, Mathieu Desnoyers wrote:
>> Actually, the field may contain the value 0 even if 0 is not part of the
>> possible cpumask. So forget what I just said about being guaranteed to
>> be part of the possible cpus mask.
>>
>> Thoughts ?
>>
>> Thanks,
>>
>> Mathieu
> 
> I don't have a full understanding, so I will trust you for deciding what is
> best.  I'll try to understand it, but my kernel knowledge is rather limited :)
> 
> I suggest writing a detailed description, instead of (or complementary to it)
> just using a range, since readers might wonder as I did, what nr_possible_cpus
> is (it's not really described anywhere so far).  With a worded description,
> we can later improve it if we find it not clear enough, but should be enough
> for an initial page.

After giving it some thoughts, I think the most precise description 
would be that the cpu number is guaranteed to be either 0, or the CPU 
number on which the registered thread is running. Let's not bring in 
notions of possible cpus (those come from 
/sys/devices/system/cpu/possible) unless it's absolutely required.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com