From: Wanpeng Li <kernellwp@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Wanpeng Li <wanpeng.li@hotmail.com>,
Ingo Molnar <mingo@kernel.org>, Mike Galbraith <efault@gmx.de>,
Thomas Gleixner <tglx@linutronix.de>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] x86/smp: Add irq_enter/exit() in smp_reschedule_interrupt()
Date: Mon, 17 Oct 2016 17:45:32 +0800 [thread overview]
Message-ID: <CANRm+CxSHMpF4LUfcF1U_8GXnwAo9beXM6C-3JaTpm7Eb3bxUw@mail.gmail.com> (raw)
In-Reply-To: <20161017082250.GX3568@worktop.programming.kicks-ass.net>
Cc Paolo,
2016-10-17 16:22 GMT+08:00 Peter Zijlstra <peterz@infradead.org>:
> On Mon, Oct 17, 2016 at 12:19:43PM +0800, Wanpeng Li wrote:
>> 2016-10-16 21:39 GMT+08:00 Peter Zijlstra <peterz@infradead.org>:
>
>> >> [<ffffffff9d492b95>] do_trace_write_msr+0x135/0x140
>> >> [<ffffffff9d06f860>] native_write_msr+0x20/0x30
>> >> [<ffffffff9d065fad>] native_apic_msr_eoi_write+0x1d/0x30
>> >> [<ffffffff9d05bd1d>] smp_reschedule_interrupt+0x1d/0x30
>> >> [<ffffffff9d8daec6>] reschedule_interrupt+0x96/0xa0
>
>> >> __visible void smp_reschedule_interrupt(struct pt_regs *regs)
>> >> {
>> >> + irq_enter();
>> >> ack_APIC_irq();
>> >> __smp_reschedule_interrupt();
>> >> + irq_exit();
>> >
>> > Urgh, I really hate this...
>> >
>> > So now we're making a very frequent interrupt slower because of debug
>> > code :/
>>
>> Do you have a better idea? :)
>
> Something like the below avoids all that. Paravirt will still need fixing.
kvm_guest_apic_eoi_write
-> native_apic_msr_write
I think you can replace the wrmsr in native_apic_msr_write() by your
wrmsr_notrace().
Regards,
Wanpeng Li
>
> The thing is, many many smp_reschedule_interrupt() invocations don't
> actually execute anything much at all and are only send to tickle the
> return to user path (which does the actual preemption).
>
> Having to do the whole irq_enter/irq_exit dance just for this unlikely
> debug case totally blows.
>
> ---
> arch/x86/include/asm/apic.h | 2 +-
> arch/x86/include/asm/msr.h | 15 +++++++++++++++
> 2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index f5aaf6c83222..b97bfeed6456 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -196,7 +196,7 @@ static inline void native_apic_msr_write(u32 reg, u32 v)
>
> static inline void native_apic_msr_eoi_write(u32 reg, u32 v)
> {
> - wrmsr(APIC_BASE_MSR + (APIC_EOI >> 4), APIC_EOI_ACK, 0);
> + wrmsr_notrace(APIC_BASE_MSR + (APIC_EOI >> 4), APIC_EOI_ACK, 0);
> }
>
> static inline u32 native_apic_msr_read(u32 reg)
> diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
> index b5fee97813cd..45c080449d5b 100644
> --- a/arch/x86/include/asm/msr.h
> +++ b/arch/x86/include/asm/msr.h
> @@ -127,6 +127,16 @@ notrace static inline void native_write_msr(unsigned int msr,
> }
>
> /* Can be uninlined because referenced by paravirt */
> +notrace static inline void native_write_msr_notrace(unsigned int msr,
> + unsigned low, unsigned high)
> +{
> + asm volatile("1: wrmsr\n"
> + "2:\n"
> + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wrmsr_unsafe)
> + : : "c" (msr), "a"(low), "d" (high) : "memory");
> +}
> +
> +/* Can be uninlined because referenced by paravirt */
> notrace static inline int native_write_msr_safe(unsigned int msr,
> unsigned low, unsigned high)
> {
> @@ -228,6 +238,11 @@ static inline void wrmsr(unsigned msr, unsigned low, unsigned high)
> native_write_msr(msr, low, high);
> }
>
> +static inline void wrmsr_notrace(unsigned msr, unsigned low, unsigned high)
> +{
> + native_write_msr_notrace(msr, low, high);
> +}
> +
> #define rdmsrl(msr, val) \
> ((val) = native_read_msr((msr)))
>
next prev parent reply other threads:[~2016-10-17 9:45 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-14 1:48 [PATCH] x86/smp: Add irq_enter/exit() in smp_reschedule_interrupt() Wanpeng Li
2016-10-14 12:19 ` [tip:x86/urgent] " tip-bot for Wanpeng Li
2016-10-16 13:39 ` [PATCH] " Peter Zijlstra
2016-10-17 4:19 ` Wanpeng Li
2016-10-17 8:22 ` Peter Zijlstra
2016-10-17 9:45 ` Wanpeng Li [this message]
2016-10-17 10:08 ` Paolo Bonzini
2016-10-17 10:23 ` Wanpeng Li
2016-10-18 0:01 ` Wanpeng Li
2016-10-19 14:01 ` Wanpeng Li
2016-10-19 14:10 ` Paolo Bonzini
2016-10-19 14:30 ` Wanpeng Li
2016-10-24 14:32 ` Paolo Bonzini
2016-10-25 2:52 ` Wanpeng Li
2016-10-17 12:19 ` Wanpeng Li
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