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

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Message-ID: <9656909.LrxhuH3ECW@kreacher>
Date:   Fri, 08 Nov 2019 01:45:03 +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 1:28:44 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.

> 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.

Also note that u64 is naturally a scalar only.
 
> > 
> > > 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).