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Date: Mon, 4 Mar 2013 10:13:28 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: hpa@...or.com, bp@...en8.de, mingo@...hat.com, tglx@...utronix.de,
rostedt@...dmis.org, gregkh@...uxfoundation.org,
samu.kallio@...rdeencloud.com, kraman@...hat.com,
jwboyer@...hat.com, xen-devel@...ts.xen.org,
linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] mm/x86: Patch out arch_flush_lazy_mmu_mode() when
running on bare metal
On Thu, Feb 28, 2013 at 05:55:49PM -0500, Boris Ostrovsky wrote:
> Invoking arch_flush_lazy_mmu_mode() results in calls to
> preempt_enable()/disable() which may have performance impact.
>
> Since lazy MMU is not used on bare metal we can patch away
> arch_flush_lazy_mmu_mode() so that it is never called in such
> environment.
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
I am OK with this - had also run it overnight on baremetal/xen to make
sure there were no funny business.
> ---
> arch/x86/include/asm/paravirt.h | 5 ++++-
> arch/x86/include/asm/paravirt_types.h | 2 ++
> arch/x86/kernel/paravirt.c | 25 +++++++++++++------------
> arch/x86/lguest/boot.c | 1 +
> arch/x86/xen/mmu.c | 1 +
> 5 files changed, 21 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 5edd174..7361e47 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -703,7 +703,10 @@ static inline void arch_leave_lazy_mmu_mode(void)
> PVOP_VCALL0(pv_mmu_ops.lazy_mode.leave);
> }
>
> -void arch_flush_lazy_mmu_mode(void);
> +static inline void arch_flush_lazy_mmu_mode(void)
> +{
> + PVOP_VCALL0(pv_mmu_ops.lazy_mode.flush);
> +}
>
> static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx,
> phys_addr_t phys, pgprot_t flags)
> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> index 142236e..b3b0ec1 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -91,6 +91,7 @@ struct pv_lazy_ops {
> /* Set deferred update mode, used for batching operations. */
> void (*enter)(void);
> void (*leave)(void);
> + void (*flush)(void);
> };
>
> struct pv_time_ops {
> @@ -679,6 +680,7 @@ void paravirt_end_context_switch(struct task_struct *next);
>
> void paravirt_enter_lazy_mmu(void);
> void paravirt_leave_lazy_mmu(void);
> +void paravirt_flush_lazy_mmu(void);
>
> void _paravirt_nop(void);
> u32 _paravirt_ident_32(u32);
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index 17fff18..8bfb335 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -263,6 +263,18 @@ void paravirt_leave_lazy_mmu(void)
> leave_lazy(PARAVIRT_LAZY_MMU);
> }
>
> +void paravirt_flush_lazy_mmu(void)
> +{
> + preempt_disable();
> +
> + if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
> + arch_leave_lazy_mmu_mode();
> + arch_enter_lazy_mmu_mode();
> + }
> +
> + preempt_enable();
> +}
> +
> void paravirt_start_context_switch(struct task_struct *prev)
> {
> BUG_ON(preemptible());
> @@ -292,18 +304,6 @@ enum paravirt_lazy_mode paravirt_get_lazy_mode(void)
> return this_cpu_read(paravirt_lazy_mode);
> }
>
> -void arch_flush_lazy_mmu_mode(void)
> -{
> - preempt_disable();
> -
> - if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
> - arch_leave_lazy_mmu_mode();
> - arch_enter_lazy_mmu_mode();
> - }
> -
> - preempt_enable();
> -}
> -
> struct pv_info pv_info = {
> .name = "bare hardware",
> .paravirt_enabled = 0,
> @@ -475,6 +475,7 @@ struct pv_mmu_ops pv_mmu_ops = {
> .lazy_mode = {
> .enter = paravirt_nop,
> .leave = paravirt_nop,
> + .flush = paravirt_nop,
> },
>
> .set_fixmap = native_set_fixmap,
> diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
> index 1cbd89c..7114c63 100644
> --- a/arch/x86/lguest/boot.c
> +++ b/arch/x86/lguest/boot.c
> @@ -1334,6 +1334,7 @@ __init void lguest_init(void)
> pv_mmu_ops.read_cr3 = lguest_read_cr3;
> pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
> pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mmu_mode;
> + pv_mmu_ops.lazy_mode.flush = paravirt_flush_lazy_mmu;
> pv_mmu_ops.pte_update = lguest_pte_update;
> pv_mmu_ops.pte_update_defer = lguest_pte_update;
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index e8e3493..f4f4105 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -2197,6 +2197,7 @@ static const struct pv_mmu_ops xen_mmu_ops __initconst = {
> .lazy_mode = {
> .enter = paravirt_enter_lazy_mmu,
> .leave = xen_leave_lazy_mmu,
> + .flush = paravirt_flush_lazy_mmu,
> },
>
> .set_fixmap = xen_set_fixmap,
> --
> 1.8.1.2
>
--
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