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Message-ID: <6348991.dSJoU6Kmcj@kreacher>
Date: Fri, 08 Nov 2019 02:34:48 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
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 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?
> >
> > > >
> > > > > In the mean time, can you please consider patches 12-14?
> > > >
> > > > I cannot find drivers/platform/x86/intel_cht_int33fe_typec.c in the mainline,
> > > > so I cannot apply patch [13/15] now and I'm not sure how useful it would be
> > > > to apply patches [10,12/15] without the other two.
> > >
> > > Hmm, drivers/platform/x86/intel_cht_int33fe_typec.c used to be
> > > drivers/platform/x86/intel_cht_int33fe.c I think.
> > >
> > > I can either regenerate against your tree instead of -next (but then
> > > there will be merge conflict) or we could postpone #13 and #14 (or #5
> > > and #6 in v7) till after merge window.
> > >
> > > Please let me know.
> >
> > I'd rather postpone the whole series to until the dependencies are in,
> > which may be during the merge window (e.g. if this happens during the
> > first week of it, waiting for another extra week just for the merge
> > window to end is not quite useful IMO).
>
> Hmm, OK, but I am not sure why we can't apply new functionality now and
> get cleanup patches in afterwards...
Because that's harder to follow from the history perspective and makes no
real difference in the end of the day.
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