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Date: Tue, 29 Nov 2016 22:15:12 +0100 From: Borislav Petkov <bp@...e.de> To: Brice Goglin <Brice.Goglin@...ia.fr> Cc: LKML <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: AMD Bulldozer topology regression since 4.6 On Tue, Nov 29, 2016 at 10:02:00PM +0100, Brice Goglin wrote: > However thread_siblings isn't back to where it was in 4.5. Now we have a > single bit in each thread_siblings mask. That's correct with respect to > the sysfs topology documentation. In 4.5, there were two bits (one for > each core of the compute unit), which was wrong (cores with different > core_ids shouldn't appear in each other thread_siblings). I assumed that > these processors had to break the sysfs topology documentation to expose > the concept of "dual-core compute-unit" which somehow sits between > hyperthreading and dual-core. This is exactly the problem - there's never proper fitting of the compute unit "ideology" in the whole topology view. So what we're doing now is revert to the old strategy of keeping Bulldozer have core_id == thread_id. Basically, all CU threads are cores, as they're more powerful than, say, SMT threads, but they still share an FPU. So it is a different kind of sharing and it's kinda, well, different. There's no other way to put it. > I personally do not care much about this regression, not sure about > other user-space tools? > > Another minor related change: /proc/cpuinfo shows "cpu cores : 16" > instead of "8". Can you send me the whole thing? Offlist is fine too. Thanks. -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
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