linux-kernel - Re: [PATCH v6 11/15] software node: move small properties inline when copying

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Message-ID: <20191105235656.GW57214@dtor-ws>
Date:   Tue, 5 Nov 2019 15:56:56 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v6 11/15] software node: move small properties inline
 when copying

Hi Rafael,

On Wed, Nov 06, 2019 at 12:42:02AM +0100, Rafael J. Wysocki wrote:
> On Wednesday, October 23, 2019 10:02:29 PM CET Dmitry Torokhov wrote:
> > When copying/duplicating set of properties, move smaller properties that
> > were stored separately directly inside property entry structures. We can
> > move:
> > 
> > - up to 8 bytes from U8 arrays
> > - up to 4 words
> > - up to 2 double words
> > - one U64 value
> > - one or 2 strings.
> 
> Yes, we can do that, but how much of a difference does this really make?

Arguably not much I think, but it was pretty cheap to do.

> 
> Also, how can one distinguish between a single-value property and an inline
> array which this change?  By looking at the length?

We do not really need to distinguish between the 2. The device
properties API is typically wrap single values around arrays (i.e. it is
perfectly fine to use scalar API to fetch first element of array and use
array API to fetch a scalar). So we have property of certain type with
certain number of elements, and it can either be stored inside
property_entry structure, or outside of it. They are 2 orthogonal
concepts.

> 
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > ---
> >  drivers/base/swnode.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> > index 18a30fb3cc58..49e1108aa4b7 100644
> > --- a/drivers/base/swnode.c
> > +++ b/drivers/base/swnode.c
> > @@ -280,6 +280,16 @@ static int property_entry_copy_data(struct property_entry *dst,
> >  	if (!dst->name)
> >  		goto out_free_data;
> >  
> > +	if (!dst->is_inline && dst->length <= sizeof(dst->value)) {
> > +		/* We have an opportunity to move the data inline */
> > +		const void *tmp = dst->pointer;
> > +
> > +		memcpy(&dst->value, tmp, dst->length);
> > +		dst->is_inline = true;
> > +
> > +		kfree(tmp);
> 
> This would have been more useful if we had been able to avoid making the
> allocation altogether.

OK, I can do that and re-send this patch and the one with the tests. In
the mean time, can you please consider patches 12-14? They can be
applied even if you temporarily drop this one (#11).

Thanks.

-- 
Dmitry