Date: Thu, 16 Nov 2023 20:54:48 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: e191c0283e86 - stable/14 - Ensure 'struct thread' is aligned to a cache line Message-ID: <202311162054.3AGKsm9v054054@gitrepo.freebsd.org>
next in thread | raw e-mail | index | archive | help
The branch stable/14 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=e191c0283e8640d46ed6b725e3311d0f37f3620c commit e191c0283e8640d46ed6b725e3311d0f37f3620c Author: Olivier Certner <olce.freebsd@certner.fr> AuthorDate: 2023-10-13 08:52:31 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2023-11-16 15:07:30 +0000 Ensure 'struct thread' is aligned to a cache line Using the new UMA_ALIGN_CACHE_AND_MASK() facility, which allows to simultaneously guarantee a minimum of 32 bytes of alignment (the 5 lower bits are always 0). For the record, to this day, here's a (possibly non-exhaustive) list of synchronization primitives using lower bits to store flags in pointers to thread structures: - lockmgr, rwlock and sx all use the 5 bits directly. - rmlock indirectly relies on sx, so can use the 5 bits. - mtx (non-spin) relies on the 3 lower bits. Reviewed by: markj, kib MFC after: 2 week Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D42266 (cherry picked from commit 7d1469e555bdce32b3dfc898478ae5564d5072b1) --- sys/kern/kern_thread.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/sys/kern/kern_thread.c b/sys/kern/kern_thread.c index 4175d1594af4..d8ba94925fec 100644 --- a/sys/kern/kern_thread.c +++ b/sys/kern/kern_thread.c @@ -568,9 +568,15 @@ threadinit(void) if (tid0 != THREAD0_TID) panic("tid0 %d != %d\n", tid0, THREAD0_TID); + /* + * Thread structures are specially aligned so that (at least) the + * 5 lower bits of a pointer to 'struct thead' must be 0. These bits + * are used by synchronization primitives to store flags in pointers to + * such structures. + */ thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(), thread_ctor, thread_dtor, thread_init, thread_fini, - 32 - 1, UMA_ZONE_NOFREE); + UMA_ALIGN_CACHE_AND_MASK(32 - 1), UMA_ZONE_NOFREE); tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash); tidhashlock = (tidhash + 1) / 64; if (tidhashlock > 0)
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?202311162054.3AGKsm9v054054>