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List:       gentoo-dev
Subject:    Re: [gentoo-dev] [PATCH] cargo.eclass: use CARGO_CRATE_URIS if already available
From:       Sam James <sam () gentoo ! org>
Date:       2023-07-31 12:44:36
Message-ID: 87zg3cb680.fsf () gentoo ! org
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Michał Górny <mgorny@gentoo.org> writes:

> On Mon, 2023-07-31 at 12:41 +0200, Florian Schmaus wrote:
> > With 59dbfb80f748 ("cargo.eclass: Add variable alternative to
> > $(cargo_crate_uris)") the _cargo_set_crate_uris function was
> > introduced. This function runs when the elcass is inherited and sets
> > CARGO_CRATE_URIS.
> > 
> > Ebuilds that use $(cargo_crate_uris) in SRC_URI will again invoke this
> > function, even though CARGO_CRATE_URIS is already set. Avoiding this
> > unnecessary computation reduces the ebuild source time of
> > app-shells/nushell-0.83.0 from 21 ms to 14 ms.
> > 
> > This is a significant reduction when compared to the variable-setting
> > alternative that the commit 59dbfb80f748 ("cargo.eclass: Add variable
> > alternative to $(cargo_crate_uris)") introduced. Using the
> > variable-setting approach would reduce the ebuild source time only by a
> > little bit more than one millisecond.
> > 
> > Using
> > 
> > pk pkg source --bench 10s '=app-shells/nushell-0.83.0'
> > 
> > as benchmark, yields
> > 
> > > > Cached CARGO_CRATE_URIS | Non-Cached CARGO_CRATE_URIS |
> > > ---------------------------+-------------------------+-----------------------------|
> > >  $(cargo_crate_uris)       | mean: 14.189ms          | mean: 21.445ms           \
> > > | variable-setting approach | mean: 12.822ms          | mean: 12.852ms          \
> > > |
> > 
> > full benchmark output
> > 
> > > > Cached CARGO_CRATE_URIS (this commit)                            | Non-Cached \
> > > > CARGO_CRATE_URIS                                      |
> > > ---------------------------+---------------------------------------------------- \
> > > --------------+------------------------------------------------------------------|
> > >  $(cargo_crate_uris)       | mean: 14.189ms, min: 13.646ms, max: 15.103ms, σ = \
> > > 149 µs, N = 705 | mean: 21.445ms, min: 20.79ms,  max: 22.832ms, σ = 228 µs, N \
> > > = 467 | variable-setting approach | mean: 12.822ms, min: 12.41ms,  max: \
> > > 13.909ms, σ = 165 µs, N = 780 | mean: 12.852ms, min: 12.367ms, max: 15.437ms, \
> > > σ = 227 µs, N = 779 |
> > 
> > Signed-off-by: Florian Schmaus <flow@gentoo.org>
> > ---
> > eclass/cargo.eclass | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> > 
> > diff --git a/eclass/cargo.eclass b/eclass/cargo.eclass
> > index 70b6008d9cd8..5d6911801097 100644
> > --- a/eclass/cargo.eclass
> > +++ b/eclass/cargo.eclass
> > @@ -240,6 +240,14 @@ _cargo_set_crate_uris "${CRATES}"
> > # Constructs a list of crates from its arguments.
> > # If no arguments are provided, it uses the CRATES variable.
> > cargo_crate_uris() {
> > +	# Use already existing value for CARGO_CRATE_URIS, computed by
> > +	# _cargo_set_crate_uris, when this function is invoked without
> > +	# arguments.
> > +	if [[ $# -eq 0 && -n "${CARGO_CRATE_URIS}" ]]; then
> > +		echo "${CARGO_CRATE_URIS}"
> > +		return
> > +	fi
> > +
> > 	local crates=${*-${CRATES}}
> > 	if [[ -z ${crates} ]]; then
> > 		eerror "CRATES variable is not defined and nothing passed as argument"
> 
> This incorrectly assumes that the value of CRATES did not change which
> isn't guaranteed anywhere.

Ah, thanks! Now I remember - we discussed it before and rejected it for
this reason.


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