Messages in this thread | | | Date | Fri, 19 Sep 2014 12:24:16 -0400 | From | Peter Hurley <> | Subject | Re: Kernel bug 60770 |
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On 08/28/2014 09:53 AM, Mike Galbraith wrote: > On Thu, 2014-08-28 at 09:23 -0400, Josh Boyer wrote: >> On Sat, Aug 16, 2014 at 10:33 AM, Josh Boyer <jwboyer@fedoraproject.org> wrote: >>> Hi Len, >>> >>> Kernel bug https://bugzilla.kernel.org/show_bug.cgi?id=60770 is marked >>> as closed, but there is a patch that at least one user seems to need >>> to get things booting properly. It was sent upstream a while ago: >>> >>> http://marc.info/?l=linux-kernel&m=138976439211647&w=2 >>> >>> but has never made it into the kernel. Do you know why this is or >>> what happened to the patch? >> >> Adding Peter and Ingo. Len seems to be MIA or otherwise occupied. >> >> Peter and Ingo, and thoughts on the bug/thread above? > > That patch needs some bend adjustment, now looks like below here. > > Patch also has a secondary benefit for core2 boxen, when booted > processor.max_cstate=1, box can still use mwait. > > Subject: [PATCH REGRESSION FIX] x86 idle: restore mwait_idle() > From: Len Brown <lenb@kernel.org> > Date: Wed, 15 Jan 2014 00:37:34 -0500 > > From: Len Brown <len.brown@intel.com> > > In Linux-3.9 we removed the mwait_idle() loop: > 'x86 idle: remove mwait_idle() and "idle=mwait" cmdline param' > (69fb3676df3329a7142803bb3502fa59dc0db2e3) > > The reasoning was that modern machines should be sufficiently > happy during the boot process using the default_idle() HALT loop, > until cpuidle loads and either acpi_idle or intel_idle > invoke the newer MWAIT-with-hints idle loop. > > But two machines reported problems: > 1. Certain Core2-era machines support MWAIT-C1 and HALT only. > MWAIT-C1 is preferred for optimal power and performance. > But if they support just C1, cpuidle never loads and > so they use the boot-time default idle loop forever. > > 2. Some laptops will boot-hang if HALT is used, > but will boot successfully if MWAIT is used. > This appears to be a hidden assumption in BIOS SMI, > that is presumably valid on the proprietary OS > where the BIOS was validated. > > https://bugzilla.kernel.org/show_bug.cgi?id=60770 > > So here we effectively revert the patch above, restoring > the mwait_idle() loop. However, we don't bother restoring > the idle=mwait cmdline parameter, since it appears to add > no value. > > Maintainer notes: > For 3.9, simply revert 69fb3676df > for 3.10, patch -F3 applies, fuzz needed due to __cpuinit use in context > For 3.11, 3.12, 3.13, this patch applies cleanly > > Mike: add clflush barriers and resched IPI avoidance.
Mike,
The changes for clflush don't build prior to 3.17-rcX; X86_BUG_CLFLUSH_MONITOR was X86_FEATURE_CLFLUSH_MONITOR prior to commit 9b13a93df267af681a66a6a738bf1af10102da7d, 'x86, cpufeature: Convert more "features" to bugs'.
Len,
FWIW, I tested this patch on a dual-socket Xeon E5420, and nothing died :) The change in core temps was not statistically significant though, and I don't have more accurate testing gear for monitoring cpu power consumption.
Regards, Peter Hurley
> Cc: Mike Galbraith <bitbucket@online.de> > Cc: Ian Malone <ibmalone@gmail.com> > Cc: Josh Boyer <jwboyer@redhat.com> > Cc: <stable@vger.kernel.org> # 3.9, 3.10, 3.11, 3.12, 3.13 > Signed-off-by: Len Brown <len.brown@intel.com> > Signed-off-by: Mike Galbraith <bitbucket@online.de> > --- > arch/x86/include/asm/mwait.h | 8 ++++++ > arch/x86/kernel/process.c | 50 +++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 58 insertions(+) > > --- a/arch/x86/include/asm/mwait.h > +++ b/arch/x86/include/asm/mwait.h > @@ -30,6 +30,14 @@ static inline void __mwait(unsigned long > :: "a" (eax), "c" (ecx)); > } > > +static inline void __sti_mwait(unsigned long eax, unsigned long ecx) > +{ > + trace_hardirqs_on(); > + /* "mwait %eax, %ecx;" */ > + asm volatile("sti; .byte 0x0f, 0x01, 0xc9;" > + :: "a" (eax), "c" (ecx)); > +} > + > /* > * This uses new MONITOR/MWAIT instructions on P4 processors with PNI, > * which can obviate IPI to trigger checking of need_resched. > --- a/arch/x86/kernel/process.c > +++ b/arch/x86/kernel/process.c > @@ -28,6 +28,7 @@ > #include <asm/fpu-internal.h> > #include <asm/debugreg.h> > #include <asm/nmi.h> > +#include <asm/mwait.h> > > /* > * per-CPU TSS segments. Threads are completely 'soft' on Linux, > @@ -396,6 +397,52 @@ static void amd_e400_idle(void) > default_idle(); > } > > +/* > + * Intel Core2 and older machines prefer MWAIT over HALT for C1. > + * We can't rely on cpuidle installing MWAIT, because it will not load > + * on systems that support only C1 -- so the boot default must be MWAIT. > + * > + * Some AMD machines are the opposite, they depend on using HALT. > + * > + * So for default C1, which is used during boot until cpuidle loads, > + * use MWAIT-C1 on Intel HW that has it, else use HALT. > + */ > +static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c) > +{ > + if (c->x86_vendor != X86_VENDOR_INTEL) > + return 0; > + > + if (!cpu_has(c, X86_FEATURE_MWAIT)) > + return 0; > + > + return 1; > +} > + > +/* > + * MONITOR/MWAIT with no hints, used for default default C1 state. > + * This invokes MWAIT with interrutps enabled and no flags, > + * which is backwards compatible with the original MWAIT implementation. > + */ > + > +static void mwait_idle(void) > +{ > + if (!current_set_polling_and_test()) { > + if (static_cpu_has_bug(X86_BUG_CLFLUSH_MONITOR)) { > + mb(); > + clflush((void *)¤t_thread_info()->flags); > + mb(); > + } > + > + __monitor((void *)¤t_thread_info()->flags, 0, 0); > + if (!need_resched()) > + __sti_mwait(0, 0); > + else > + local_irq_enable(); > + } else > + local_irq_enable(); > + current_clr_polling(); > +} > + > void select_idle_routine(const struct cpuinfo_x86 *c) > { > #ifdef CONFIG_SMP > @@ -409,6 +456,9 @@ void select_idle_routine(const struct cp > /* E400: APIC timer interrupt does not wake up CPU from C1e */ > pr_info("using AMD E400 aware idle routine\n"); > x86_idle = amd_e400_idle; > + } else if (prefer_mwait_c1_over_halt(c)) { > + pr_info("using mwait in idle threads\n"); > + x86_idle = mwait_idle; > } else > x86_idle = default_idle; > }
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