From: Jeremy Linton <jeremy.linton@arm.com>
To: John Garry <john.garry@huawei.com>,
Valentin Schneider <valentin.schneider@arm.com>,
linux-arm-kernel@lists.infradead.org
Cc: linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
catalin.marinas@arm.com, will.deacon@arm.com, rjw@rjwysocki.net,
sudeep.holla@arm.com, lenb@kernel.org
Subject: Re: [PATCH v2 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag
Date: Fri, 28 Jun 2019 10:21:49 -0500 [thread overview]
Message-ID: <b7877a38-6c30-af7d-f627-1618684afb55@arm.com> (raw)
In-Reply-To: <63f6c6a8-9d79-ae75-3c15-96bded9b14e4@huawei.com>
Hi,
On 6/19/19 4:15 AM, John Garry wrote:
> On 18/06/2019 22:28, Jeremy Linton wrote:
>> Hi,
>>
>> On 6/18/19 12:23 PM, John Garry wrote:
>>> On 18/06/2019 15:40, Valentin Schneider wrote:
>>>> On 18/06/2019 15:21, Jeremy Linton wrote:
>>>> [...]
>>>>>>> + * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be
>>>>>>> found or
>>>>>>> + * the table revision isn't new enough.
>>>>>>> + * Otherwise returns flag value
>>>>>>> + */
>>>>>>
>>>>>> Nit: strictly speaking we're not returning the flag value but its
>>>>>> mask
>>>>>> applied to the flags field. I don't think anyone will care about
>>>>>> getting
>>>>>> the actual flag value, but it should be made obvious in the doc:
>>>>>
>>>>> Or I clarify the code to actually do what the comments says. Maybe
>>>>> that is what John G was also pointing out too?
>>>>>
>>>
>>> No, I was just saying that the kernel topology can be broken without
>>> this series.
>>>
>>>>
>>>> Mmm I didn't find any reply from John regarding this in v1, but I
>>>> wouldn't
>>>> mind either way, as long as the doc & code are aligned.
>>>>
>>>
>>> BTW, to me, function acpi_pptt_cpu_is_thread() seems to try to do too
>>> much, i.e. check if the PPTT is new enough to support the thread flag
>>> and also check if it is set for a specific cpu. I'd consider separate
>>> functions here.
>>
>
> Hi,
>
>> ? Your suggesting replacing the
>>
>
> I am not saying definitely that this should be changed, it's just that
> acpi_pptt_cpu_is_thread() returning false, true, or "no entry" is not a
> typical API format.
>
> How about acpi_pptt_support_thread_info(cpu) and
> acpi_pptt_cpu_is_threaded(cpu), both returning false/true only?
I'm not sure we want to be exporting what is effectively a version check
into the rest of the code. Plus, AFAIK it doesn't really simplify
anything except the case of ACPI machines with revision 1 PPTTs, because
those would only be doing a single check and assuming the state of the
MT bit. That MT check is suspect anyway, although AFAIK it gets the
right answer on all machines that predate ACPI 6.3..
>
> None of this is ideal.
>
> BTW, Have you audited which arm64 systems have MT bit set legitimately?
Not formally, given I don't have access to everything available.
>
>>
>> if (table->revision >= rev)
>
> I know that checking the table revision is not on the fast path, but it
> seems unnecessarily inefficient to always read it this way, I mean
> calling acpi_table_get().
>
> Can you have a static value for the table revision? Or is this just how
> other table info is accessed in ACPI code?
Yes caching the revision internally would save a get/put per core, for
older machines. I don't think its a big deal in normal operation but its
a couple extra lines so...
I will post it with an internally cached saved_pptt_rev. That will save
CPU count get/puts in the case where the revision isn't new enough.
>
>> cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
>>
>> check with
>>
>> if (revision_check(table, rev))
>> cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
>>
>>
>> and a function like
>>
>> static int revision_check(acpixxxx *table, int rev)
>> {
>> return (table->revision >= rev);
>> }
>>
>> Although, frankly if one were to do this, it should probably be a macro
>> with the table type, and used in the dozen or so other places I found
>> doing similar checks (spcr, iort, etc).
>>
>> Or something else?
>>
>>
>>
>>
>
> thanks,
> John
next prev parent reply other threads:[~2019-06-28 15:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-14 22:31 [PATCH v2 0/2] arm64/PPTT ACPI 6.3 thread flag support Jeremy Linton
2019-06-14 22:31 ` [PATCH v2 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag Jeremy Linton
2019-06-17 12:34 ` Valentin Schneider
2019-06-18 14:21 ` Jeremy Linton
2019-06-18 14:40 ` Valentin Schneider
2019-06-18 17:23 ` John Garry
2019-06-18 21:28 ` Jeremy Linton
2019-06-19 9:15 ` John Garry
2019-06-28 15:21 ` Jeremy Linton [this message]
2019-06-25 15:20 ` Sudeep Holla
2019-06-14 22:31 ` [PATCH v2 2/2] arm64: topology: Use PPTT to determine if PE is a thread Jeremy Linton
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=b7877a38-6c30-af7d-f627-1618684afb55@arm.com \
--to=jeremy.linton@arm.com \
--cc=catalin.marinas@arm.com \
--cc=john.garry@huawei.com \
--cc=lenb@kernel.org \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=rjw@rjwysocki.net \
--cc=sudeep.holla@arm.com \
--cc=valentin.schneider@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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).