linux-kernel - Re: [PATCH 1/5] ACPI: sysfs: convert utf-16 from

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Date: Mon, 17 Jun 2024 21:20:17 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, 
	Robert Moore <robert.moore@...el.com>, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, acpica-devel@...ts.linux.dev
Subject: Re: [PATCH 1/5] ACPI: sysfs: convert utf-16 from _STR to utf-8 only once

On Mon, Jun 17, 2024 at 8:57 PM Thomas Weißschuh <linux@...ssschuh.net> wrote:
>
> On 2024-06-17 20:43:03+0000, Rafael J. Wysocki wrote:
> > On Mon, Jun 17, 2024 at 8:37 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > >
> > > On Thu, Jun 13, 2024 at 10:15 PM Thomas Weißschuh <linux@...ssschuh.net> wrote:
> > > >
> > > > The ACPI _STR method returns an UTF-16 string that is converted to utf-8
> > > > before printing it in sysfs.
> > > > Currently this conversion is performed every time the "description"
> > > > sysfs attribute is read, which is not necessary.
> > >
> > > Why is it a problem, though?
>
> It's not a real problem, mostly it made the following changes simpler.
>
> > > How many devices have _STR and how much of the time is it used?
> > >
> > > Hint: On the system I'm sitting in front of, the answer is 0 and never.
> >
> > This was actually factually incorrect, sorry.
> >
> > The correct answer is 12 out of 247 and very rarely (if at all).
> > Which doesn't really change the point IMO.
> >
> > > So Is it really worth adding an _STR string pointer to every struct acpi_device?
>
> The string pointer replaces a 'union acpi_object *str_obj', so no new
> space is used.
> Also in case the device _STR is present the new code uses less memory, as
> it doesn't need the full union and stores utf-8 instead of utf-16.
> (Plus a few more cycles for the preemptive conversion)
>
> In case no _STR is present both CPU and memory costs are identical.

OK

> Anyways, I don't really care about this and can also try to drop this
> patch if you prefer.
> Or drop the 'union acpi_device *' from the struct completely at your
> preference.

No, this is fine as is, thanks.