From mboxrd@z Thu Jan 1 00:00:00 1970 From: james.hogan@imgtec.com (James Hogan) Date: Mon, 4 Jan 2016 16:04:55 +0000 Subject: [PATCH v2 20/32] metag: define __smp_xxx In-Reply-To: <20160104153036.GG6344@twins.programming.kicks-ass.net> References: <1451572003-2440-1-git-send-email-mst@redhat.com> <1451572003-2440-21-git-send-email-mst@redhat.com> <20160104134128.GZ6344@twins.programming.kicks-ass.net> <20160104152558.GD17861@jhogan-linux.le.imgtec.org> <20160104153036.GG6344@twins.programming.kicks-ass.net> Message-ID: <20160104160455.GE17861@jhogan-linux.le.imgtec.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jan 04, 2016 at 04:30:36PM +0100, Peter Zijlstra wrote: > On Mon, Jan 04, 2016 at 03:25:58PM +0000, James Hogan wrote: > > It is used along with the metag specific __global_lock1() (global > > voluntary lock between hw threads) whenever a write is performed, and by > > smp_mb/smp_rmb to try to catch other cases, but I've never been > > confident this fixes every single corner case, since there could be > > other places where multiple CPUs perform unsynchronised writes to the > > same memory location, and expect cache not to become incoherent at that > > location. > > Ah, yuck, I thought blackfin was the only one attempting !coherent SMP. > And yes, this is bound to break in lots of places in subtle ways. We > very much assume cache coherency for SMP in generic code. Well, its usually completely coherent, its just a bit dodgy in a particular hardware corner case, which was pretty hard to hit, even without these workarounds. > > > It seemed to be sufficient to achieve stability however, and SMP on Meta > > Linux never made it into a product anyway, since the other hw thread > > tended to be used for RTOS stuff, so it didn't seem worth extending the > > generic barrier API for it. > > *phew*, should we take it out then, just to be sure nobody accidentally > tries to use it then? SMP support on this SoC you mean? I doubt it'll be a problem tbh, and it'd work fine in QEMU when emulating this SoC, so I'd prefer to keep it in. Cheers James -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: Digital signature URL: