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Date: Thu, 7 Nov 2019 19:45:14 -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
On Fri, Nov 08, 2019 at 02:34:48AM +0100, Rafael J. Wysocki wrote:
> On Friday, November 8, 2019 1:49:46 AM CET Dmitry Torokhov wrote:
> > On Fri, Nov 08, 2019 at 01:45:03AM +0100, Rafael J. Wysocki wrote:
> > > On Friday, November 8, 2019 1:28:44 AM CET Dmitry Torokhov wrote:
> > > > On Fri, Nov 08, 2019 at 01:04:31AM +0100, Rafael J. Wysocki wrote:
> > > > > On Wednesday, November 6, 2019 12:56:56 AM CET Dmitry Torokhov wrote:
> > > > > > 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.
> > > > >
> > > > > But if you do that, IMO it would be prudent to extend the definition of
> > > > > struct property_entry like this:
> > > > >
> > > > > struct property_entry {
> > > > > const char *name;
> > > > > size_t length;
> > > > > bool is_array;
> > > > > enum dev_prop_type type;
> > > > > union {
> > > > > union {
> > > > > const u8 *u8_data;
> > > > > const u16 *u16_data;
> > > > > const u32 *u32_data;
> > > > > const u64 *u64_data;
> > > > > const char * const *str;
> > > > > } pointer;
> > > > > union {
> > > > > u8 u8_data;
> > > > > u16 u16_data;
> > > > > u32 u32_data;
> > > > > u64 u64_data;
> > > > > const char *str;
> > > > > + u8 u8_buf[sizeof(u64)];
> > > > > + u16 u16_buf[sizeof(u64)/sizeof(u16)];
> > > > > + u32 u32_buf[sizeof(u64)/sizeof(u32)];
> > > > > + char char_buf[sizeof(u64)];
> > > > > } value;
> > > > > };
> > > > > };
> > > > >
> > > > > to make it clear that the value field is going to be used as an array in
> > > > > some cases.
> > > >
> > > > Sorry, just sent out updated series before receiving your email. I can
> > > > cook up new patch cleaning this.
> > >
> > > I'd prefer a new version of the series, honestly.
> >
> > OK, sure.
> >
> > >
> > > > I think we can drop scalars and only have arrays and have initializers use
> > > > <type>_data[0] to create initial property entries.
> > >
> > > Why [0]? IMO it is better to use the exact size (which is known) in this
> > > particular case.
> >
> > diff --git a/include/linux/property.h b/include/linux/property.h
> > index b315fdc0ec28d..b28c81af7bb68 100644
> > --- a/include/linux/property.h
> > +++ b/include/linux/property.h
> > @@ -257,11 +257,11 @@ struct property_entry {
> > union {
> > const void *pointer;
> > union {
> > - u8 u8_data;
> > - u16 u16_data;
> > - u32 u32_data;
> > - u64 u64_data;
> > - const char *str;
> > + u8 u8_data[sizeof(u64) / sizeof(u8)];
> > + u16 u16_data[sizeof(u64) / sizeof(u16)];
> > + u32 u32_data[sizeof(u64) / sizeof(u32)];
> > + u64 u64_data[sizeof(u64) / sizeof(u64)];
>
> IMO with a scalar u64 this kind of would explain itself, but with a u64 array
> it becomes somewhat confusing.
>
> > + const char *str[sizeof(u64) / sizeof(char *)];
> > } value;
> > };
> > };
> > @@ -273,7 +273,7 @@ struct property_entry {
> > */
> >
> > #define __PROPERTY_ENTRY_ELEMENT_SIZE(_elem_) \
> > - sizeof(((struct property_entry *)NULL)->value._elem_)
> > + sizeof(((struct property_entry *)NULL)->value._elem_[0])
> >
> > #define __PROPERTY_ENTRY_ARRAY_ELSIZE_LEN(_name_, _elsize_, _Type_, \
> > _val_, _len_) \
> > @@ -323,7 +323,7 @@ struct property_entry {
> > .length = __PROPERTY_ENTRY_ELEMENT_SIZE(_elem_), \
> > .is_inline = true, \
> > .type = DEV_PROP_##_Type_, \
> > - { .value = { ._elem_ = _val_ } }, \
> > + { .value = { ._elem_[0] = _val_ } }, \
> > }
> >
> > #define PROPERTY_ENTRY_U8(_name_, _val_) \
> >
> > >
> > > Also note that u64 is naturally a scalar only.
> >
> > It still can be expressed as array of 1 element.
>
> It can, but for what purpose?
Just so we do not have to special-case handling of U64 in
PROPERTY_ENTRY_Unnn() macros, as I shown in the snippet above.
--
Dmitry
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