Messages in this thread | | | From | "Ghannam, Yazen" <> | Subject | RE: [PATCH] x86/smpboot: Don't do mwait_play_dead() on AMD systems | Date | Tue, 3 Apr 2018 13:55:36 +0000 |
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> -----Original Message----- > From: Ingo Molnar <mingo.kernel.org@gmail.com> On Behalf Of Ingo Molnar > Sent: Tuesday, April 3, 2018 7:04 AM > To: Ghannam, Yazen <Yazen.Ghannam@amd.com> > 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 > > > * Yazen Ghannam <Yazen.Ghannam@amd.com> wrote: > > > From: Yazen Ghannam <yazen.ghannam@amd.com> > > > > 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 <yazen.ghannam@amd.com> > > --- > > 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 ... >
Yes, I'll drop that comment since the commit message has the explanation.
Thanks, Yazen
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