From: Nadav Amit <namit@vmware.com>
To: Juergen Gross <jgross@suse.com>
Cc: Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Borislav Petkov <bp@alien8.de>,
Peter Zijlstra <peterz@infradead.org>,
Sasha Levin <sashal@kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
xen-devel <xen-devel@lists.xenproject.org>,
Haiyang Zhang <haiyangz@microsoft.com>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Ingo Molnar <mingo@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm list <kvm@vger.kernel.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently
Date: Wed, 3 Jul 2019 17:02:36 +0000 [thread overview]
Message-ID: <A4BC0EDE-71F0-455D-964A-7250D005FB56@vmware.com> (raw)
In-Reply-To: <d89e2b57-8682-153e-33d8-98084e9983d6@suse.com>
> On Jul 3, 2019, at 7:04 AM, Juergen Gross <jgross@suse.com> wrote:
>
> On 03.07.19 01:51, Nadav Amit wrote:
>> To improve TLB shootdown performance, flush the remote and local TLBs
>> concurrently. Introduce flush_tlb_multi() that does so. Introduce
>> paravirtual versions of flush_tlb_multi() for KVM, Xen and hyper-v (Xen
>> and hyper-v are only compile-tested).
>> While the updated smp infrastructure is capable of running a function on
>> a single local core, it is not optimized for this case. The multiple
>> function calls and the indirect branch introduce some overhead, and
>> might make local TLB flushes slower than they were before the recent
>> changes.
>> Before calling the SMP infrastructure, check if only a local TLB flush
>> is needed to restore the lost performance in this common case. This
>> requires to check mm_cpumask() one more time, but unless this mask is
>> updated very frequently, this should impact performance negatively.
>> Cc: "K. Y. Srinivasan" <kys@microsoft.com>
>> Cc: Haiyang Zhang <haiyangz@microsoft.com>
>> Cc: Stephen Hemminger <sthemmin@microsoft.com>
>> Cc: Sasha Levin <sashal@kernel.org>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Borislav Petkov <bp@alien8.de>
>> Cc: x86@kernel.org
>> Cc: Juergen Gross <jgross@suse.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> Cc: linux-hyperv@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> Cc: virtualization@lists.linux-foundation.org
>> Cc: kvm@vger.kernel.org
>> Cc: xen-devel@lists.xenproject.org
>> Signed-off-by: Nadav Amit <namit@vmware.com>
>> ---
>> arch/x86/hyperv/mmu.c | 13 +++---
>> arch/x86/include/asm/paravirt.h | 6 +--
>> arch/x86/include/asm/paravirt_types.h | 4 +-
>> arch/x86/include/asm/tlbflush.h | 9 ++--
>> arch/x86/include/asm/trace/hyperv.h | 2 +-
>> arch/x86/kernel/kvm.c | 11 +++--
>> arch/x86/kernel/paravirt.c | 2 +-
>> arch/x86/mm/tlb.c | 65 ++++++++++++++++++++-------
>> arch/x86/xen/mmu_pv.c | 20 ++++++---
>> include/trace/events/xen.h | 2 +-
>> 10 files changed, 91 insertions(+), 43 deletions(-)
>
> ...
>
>> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
>> index beb44e22afdf..19e481e6e904 100644
>> --- a/arch/x86/xen/mmu_pv.c
>> +++ b/arch/x86/xen/mmu_pv.c
>> @@ -1355,8 +1355,8 @@ static void xen_flush_tlb_one_user(unsigned long addr)
>> preempt_enable();
>> }
>> -static void xen_flush_tlb_others(const struct cpumask *cpus,
>> - const struct flush_tlb_info *info)
>> +static void xen_flush_tlb_multi(const struct cpumask *cpus,
>> + const struct flush_tlb_info *info)
>> {
>> struct {
>> struct mmuext_op op;
>> @@ -1366,7 +1366,7 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
>> const size_t mc_entry_size = sizeof(args->op) +
>> sizeof(args->mask[0]) * BITS_TO_LONGS(num_possible_cpus());
>> - trace_xen_mmu_flush_tlb_others(cpus, info->mm, info->start, info->end);
>> + trace_xen_mmu_flush_tlb_multi(cpus, info->mm, info->start, info->end);
>> if (cpumask_empty(cpus))
>> return; /* nothing to do */
>> @@ -1375,9 +1375,17 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
>> args = mcs.args;
>> args->op.arg2.vcpumask = to_cpumask(args->mask);
>> - /* Remove us, and any offline CPUS. */
>> + /* Flush locally if needed and remove us */
>> + if (cpumask_test_cpu(smp_processor_id(), to_cpumask(args->mask))) {
>> + local_irq_disable();
>> + flush_tlb_func_local(info);
>
> I think this isn't the correct function for PV guests.
>
> In fact it should be much easier: just don't clear the own cpu from the
> mask, that's all what's needed. The hypervisor is just fine having the
> current cpu in the mask and it will do the right thing.
Thanks. I will do so in v3. I don’t think Hyper-V people would want to do
the same, unfortunately, since it would induce VM-exit on TLB flushes. But
if they do - I’ll be able not to expose flush_tlb_func_local().
next prev parent reply other threads:[~2019-07-03 17:02 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-02 23:51 [PATCH v2 0/9] x86: Concurrent TLB flushes Nadav Amit
2019-07-02 23:51 ` [PATCH v2 1/9] smp: Run functions concurrently in smp_call_function_many() Nadav Amit
2019-07-02 23:51 ` [PATCH v2 2/9] x86/mm/tlb: Remove reason as argument for flush_tlb_func_local() Nadav Amit
2019-07-02 23:51 ` [PATCH v2 3/9] x86/mm/tlb: Open-code on_each_cpu_cond_mask() for tlb_is_not_lazy() Nadav Amit
2019-07-02 23:51 ` [PATCH v2 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently Nadav Amit
2019-07-03 14:04 ` Juergen Gross
2019-07-03 17:02 ` Nadav Amit [this message]
2019-07-03 17:43 ` [Xen-devel] " Andrew Cooper
2019-07-03 18:09 ` Nadav Amit
2019-07-02 23:51 ` [PATCH v2 5/9] x86/mm/tlb: Privatize cpu_tlbstate Nadav Amit
2019-07-02 23:51 ` [PATCH v2 6/9] x86/mm/tlb: Do not make is_lazy dirty for no reason Nadav Amit
2019-07-02 23:51 ` [PATCH v2 7/9] cpumask: Mark functions as pure Nadav Amit
2019-07-02 23:51 ` [PATCH v2 8/9] x86/mm/tlb: Remove UV special case Nadav Amit
2019-07-09 19:50 ` Thomas Gleixner
2019-07-09 20:09 ` Russ Anderson
2019-07-09 20:29 ` Mike Travis
2019-07-09 21:09 ` Nadav Amit
2019-07-09 21:17 ` Mike Travis
2019-07-02 23:51 ` [PATCH v2 9/9] x86/mm/tlb: Remove unnecessary uses of the inline keyword Nadav Amit
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