From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755193AbeDCLD5 (ORCPT ); Tue, 3 Apr 2018 07:03:57 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:53184 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754869AbeDCLD4 (ORCPT ); Tue, 3 Apr 2018 07:03:56 -0400 X-Google-Smtp-Source: AIpwx4/YHwUaaa1jpOvOP3tiGsYy/0XJLKDLl9pHziGWdM9L4NZgQR77pGKcWeVGwUKnlMRzEmByAg== Date: Tue, 3 Apr 2018 13:03:52 +0200 From: Ingo Molnar To: Yazen Ghannam Cc: x86@kernel.org, linux-kernel@vger.kernel.org, bp@suse.de Subject: Re: [PATCH] x86/smpboot: Don't do mwait_play_dead() on AMD systems Message-ID: <20180403110352.izr2kvsd3ys4drjq@gmail.com> References: <20180402183424.48222-1-Yazen.Ghannam@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180402183424.48222-1-Yazen.Ghannam@amd.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Yazen Ghannam wrote: > From: Yazen Ghannam > > Recent AMD systems support using MWAIT for C1 state. However, MWAIT will > not allow deeper cstates than C1 on current systems. > > With play_dead() we expect the OS to use the deepest state available. > The deepest state available on AMD systems is reached through SystemIO > or HALT. If MWAIT is available, we use it instead of the other methods, > so we never reach the deepest state. > > Don't try to use MWAIT to play_dead() on AMD systems. Instead, we'll use > CPUIDLE to enter the deepest state advertised by firmware. If CPUIDLE is > not available then we fallback to HALT. > > Signed-off-by: Yazen Ghannam > --- > arch/x86/kernel/smpboot.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index ff99e2b6fc54..67cf00b25f83 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -1536,6 +1536,9 @@ static inline void mwait_play_dead(void) > void *mwait_ptr; > int i; > > + /* Don't try native MWAIT on AMD. Stick to CPUIDLE and HALT. */ > + if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) > + return; The comment should mainly explain the 'why is this done', not the 'what is done' which is pretty obvious from the code ... Thanks, Ingo