From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org
X-Spam-Level: 
X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI,
	RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_PASS
	autolearn=ham autolearn_force=no version=3.4.2
Received: (qmail 32268 invoked from network); 15 Apr 2020 09:50:51 -0000
Received-SPF:  pass (mother.openwall.net: domain of lists.openwall.com
  designates 195.42.179.200 as permitted sender)
  receiver=inbox.vuxu.org; client-ip=195.42.179.200
  envelope-from=<musl-return-15689-ml=inbox.vuxu.org@lists.openwall.com>
Received: from mother.openwall.net (195.42.179.200)
  by inbox.vuxu.org with UTF8ESMTPZ; 15 Apr 2020 09:50:51 -0000
Received: (qmail 6081 invoked by uid 550); 15 Apr 2020 09:50:49 -0000
Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm
Precedence: bulk
List-Post: <mailto:musl@lists.openwall.com>
List-Help: <mailto:musl-help@lists.openwall.com>
List-Unsubscribe: <mailto:musl-unsubscribe@lists.openwall.com>
List-Subscribe: <mailto:musl-subscribe@lists.openwall.com>
List-ID: <musl.lists.openwall.com>
Reply-To: musl@lists.openwall.com
Received: (qmail 6057 invoked from network); 15 Apr 2020 09:50:48 -0000
From: Florian Weimer <fw@deneb.enyo.de>
To: Norbert Lange <nolange79@gmail.com>
Cc: musl@lists.openwall.com,  Rich Felker <dalias@libc.org>
References: <CADYdroOZ__aFuCCBWCAOBRcH==0W-NUKH423biu217X9t6Pxeg@mail.gmail.com>
	<20200409181824.GD13749@port70.net> <87r1wwik8t.fsf@mid.deneb.enyo.de>
	<20200410010255.GN11469@brightrain.aerifal.cx>
	<877dyinzuz.fsf@mid.deneb.enyo.de>
	<20200414155522.GB11469@brightrain.aerifal.cx>
	<87wo6iknx1.fsf@mid.deneb.enyo.de>
	<CADYdroPaVEBkNLH1eLBL9ZuVtzc95ckAmu90iOjemwTwVbKKtQ@mail.gmail.com>
Date: Wed, 15 Apr 2020 11:50:36 +0200
In-Reply-To: <CADYdroPaVEBkNLH1eLBL9ZuVtzc95ckAmu90iOjemwTwVbKKtQ@mail.gmail.com>
	(Norbert Lange's message of "Wed, 15 Apr 2020 11:38:42 +0200")
Message-ID: <87o8rtjcwj.fsf@mid.deneb.enyo.de>
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [musl] [BUG] sysconf implementing _SC_NPROCESSORS_(CONF|ONLN) incorrectly

* Norbert Lange:

> How should  one deal with this?
> I understand that the semantics are vague, but given that musl now
> implements this
> function, it will make detection and fallback hard (especially as musl
> doesn't wants to be identified by the likes of macros).
>
> As it is now, just using the affinity mask definitely cant be useful,
> an application wanting that behavior should be patched to
> use that function directly.
> If musl would not define the _SC_NPROCESSORS_* macros (but still keep
> the implementation),
> this could be used for compile-time detection atleast. Enabling the
> current implementation would be
> just a matter of explicitly defining those macros.

_SC_NPROCESSORS_* as implemented in glibc is bad because those values
are not adjusted by cgroups, so it can grossly overestimate available
resources.

The cgroups interfaces themselves are not stable and very complicated.
I don't think it's a good idea to target them, especially not from
code that is expected to be linked statically into applications.

Given that, I'm not sure that glibc's way is a significant
improvement.  musl should perhaps be changed to cope more gracefully
with a sched_getaffinity failure, though (by not reporting a UP
environment by accident).