From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/8984 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: stdatomic implementation Date: Sun, 13 Dec 2015 16:25:30 +0100 Message-ID: <1450020330.317.11.camel@inria.fr> References: <1450000882.317.5.camel@inria.fr> <20151213145950.GH23362@port70.net> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-zBtouA5Yl1ECykrQzYaw" X-Trace: ger.gmane.org 1450020354 23093 80.91.229.3 (13 Dec 2015 15:25:54 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 13 Dec 2015 15:25:54 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-8997-gllmg-musl=m.gmane.org@lists.openwall.com Sun Dec 13 16:25:47 2015 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from 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Cj15cu23XZI4/826Px/xqB37z547sPH374oOvnKTsOb+1zuCoImZARM8ZiLlKkXcWOcoFRJ+Do/CwFO4e2DEe+9Ti+ZXA8ny/cU+X4bMKRZxZIVEiqXI6/+NKuUzPHb7z40ovnX3zx+Ctuq38HyuqWG7Tu+A0AAAAASUVORK5CYII= X-Mailer: Evolution 3.12.9-1+b1 Xref: news.gmane.org gmane.linux.lib.musl.general:8984 Archived-At: --=-zBtouA5Yl1ECykrQzYaw Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hello, Am Sonntag, den 13.12.2015, 15:59 +0100 schrieb Szabolcs Nagy: > * Jens Gustedt [2015-12-13 11:01:22 +0100]: > > Its integration into musl should be straight forward and remains my > > primary choice for having it distributed. You can find it at > >=20 > > stdatomic.gforge.inria.fr > >=20 >=20 > nice >=20 > i recently run into a problem that you may be interested in: > the gcc atomic builtins do not handle atomic pointer types as > expected. >=20 > T *p; > __atomic_fetch_add(&p,1); >=20 > adds 1 to (char*)p instead of sizeof(T). >=20 > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D64843 thanks, I wasn't aware of that one. FYI in a recent DR about atomics, among other things, I pointed on the missing specification of atomic_fetch_add for pointer types. I think I can safely say that the consensus among the committee for that specific problem was to say that this was just an omission in C11. Unfortunately, that DR opened a whole can of worms about atomics. I was asked to cut it down in smaller pieces that will easier to tackle with the DR process. > > Under the hood it uses a new lock algorithm based on futex waits for > > the slow path, that has proven to be more efficient than anything else > > that I looked at: musl's internal lock, mtx_t or pthread_mutex_t, or > > spinlocks. You can find a discussion of that at > >=20 > > https://hal.inria.fr/hal-01236734 > >=20 > > Before I go (more) public with this, I would very much like to hear > > what you think. >=20 > i havent read the paper yet but it is worth noting that > glibc implements weaker pthread semantics than musl, so > on glibc pthread_mutex_lock/unlock is acquire/release. > (which makes pthread_mutex_trylock non-conforming, but > it's closer to the c11 semantics, same for spinlocks). Hm, interesting. From our lengthy discussion, here, about mutexes and conditions last year I had the vague impression that for musl also this was more-or-less acquire/release, at least to completely seq_cst, either. > so it would be interesting to benchmark against glibc > primitives too. Yes, probably, also it would be interesting to have it on more architectures and for more test cases. Thanks Jens --=20 :: INRIA Nancy Grand Est ::: Camus ::::::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt :: --=-zBtouA5Yl1ECykrQzYaw Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iEYEABECAAYFAlZtjeoACgkQD9PoadrVN+IIJgCfRzDU6gveosoS5H5l5D1IJ6pK il4An0PF3/ebntCLpi3fz4G4zSB4LONd =pmx3 -----END PGP SIGNATURE----- --=-zBtouA5Yl1ECykrQzYaw--