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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Rik van Riel <riel@surriel.com>,
	Andy Lutomirski <luto@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	Mike Galbraith <efault@gmx.de>, kernel-team <kernel-team@fb.com>,
	Ingo Molnar <mingo@kernel.org>,
	Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH 4/7] x86,tlb: make lazy TLB mode lazier
Date: Fri, 20 Jul 2018 12:18:28 +0200	[thread overview]
Message-ID: <87fu0etdl7.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20180720094906.GP2494@hirez.programming.kicks-ass.net> (Peter Zijlstra's message of "Fri, 20 Jul 2018 11:49:06 +0200")

Peter Zijlstra <peterz@infradead.org> writes:

> On Fri, Jul 20, 2018 at 10:02:10AM +0200, Vitaly Kuznetsov wrote:
>> Andy Lutomirski <luto@amacapital.net> writes:
>> 
>> > [I added PeterZ and Vitaly -- can you see any way in which this would
>> > break something obscure?  I don't.]
>> 
>> Thanks for CCing me,
>> 
>> I don't see how this can break things either. At first glance, however,
>> I'm afraid we can add performance penalty to virtualized guests which
>> don't use native_flush_tlb_others() (Hyper-V, KVM): we will be reloading
>> CR3 without a need as we don't look at lazy mode in PV tlb flush
>> functions.
>> 
>> We can either check to switch_mm_irqs_off() that
>> native_flush_tlb_others() is in use or teach PV tlb flush functions to
>> look at lazy mode too.
>
> As Rik noted elsewhere in the thread, kvm_flush_tlb_others() ends up
> calling native_tlb_flush_others() for all running vcpu threads.

Ah, right!

>
> The Hyper-V thing is magical, we can't really do anything about it
> there. Let them worry about it.

Well, we kinda know how this magic works: we just ask the hypervisor to
flush TLB for us (if the particular vCPU is running) :-) Anyway, nothing
stops us from duplicating the logic regarding lazy mode from
native_flush_tlb_others() to hyperv_flush_tlb_others(): if TLB state is
lazy omit TLB flush.

-- 
  Vitaly

  reply	other threads:[~2018-07-20 10:18 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-16 19:03 [PATCH v6 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-16 19:03 ` [PATCH 1/7] mm: allocate mm_cpumask dynamically based on nr_cpu_ids Rik van Riel
2018-07-17  9:33   ` [tip:x86/mm] mm: Allocate the mm_cpumask (mm->cpu_bitmap[]) " tip-bot for Rik van Riel
2018-08-04 22:28   ` [PATCH 1/7] mm: allocate mm_cpumask " Guenter Roeck
2018-07-16 19:03 ` [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time Rik van Riel
2018-07-17  9:34   ` [tip:x86/mm] x86/mm/tlb: Leave " tip-bot for Rik van Riel
2018-07-17 11:46     ` Peter Zijlstra
2018-07-25  1:00       ` Anders Roxell
2018-08-16  1:54   ` [PATCH 2/7] x86,tlb: leave " Andy Lutomirski
2018-08-16  5:31     ` Rik van Riel
2018-07-16 19:03 ` [PATCH 3/7] x86,mm: restructure switch_mm_irqs_off Rik van Riel
2018-07-17  9:34   ` [tip:x86/mm] x86/mm/tlb: Restructure switch_mm_irqs_off() tip-bot for Rik van Riel
2018-10-09 14:58   ` tip-bot for Rik van Riel
2018-07-16 19:03 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-07-17  9:35   ` [tip:x86/mm] x86/mm/tlb: Make " tip-bot for Rik van Riel
2018-07-17 11:33     ` Peter Zijlstra
2018-07-18 15:33       ` Rik van Riel
2018-07-18 16:00         ` Peter Zijlstra
     [not found]           ` <081E558D-DB34-4A18-A35C-896BC47F6EBA@surriel.com>
2018-07-18 18:23             ` Peter Zijlstra
2018-07-18 18:51               ` Rik van Riel
2018-07-19  9:13                 ` Peter Zijlstra
2018-07-17 20:04   ` [PATCH 4/7] x86,tlb: make " Andy Lutomirski
     [not found]     ` <FF977B78-140F-4787-AA57-0EA934017D85@surriel.com>
2018-07-17 21:29       ` Andy Lutomirski
2018-07-17 22:05         ` Rik van Riel
2018-07-17 22:27           ` Andy Lutomirski
2018-07-18 20:58     ` Rik van Riel
2018-07-18 23:13       ` Andy Lutomirski
     [not found]         ` <B976CC13-D014-433A-83DE-F8DF9AB4F421@surriel.com>
2018-07-19 16:45           ` Andy Lutomirski
2018-07-19 17:04             ` Andy Lutomirski
2018-07-19 17:04               ` Andy Lutomirski
2018-07-20  4:57               ` Benjamin Herrenschmidt
2018-07-20  8:30               ` Peter Zijlstra
2018-07-23 12:26                 ` Rik van Riel
2018-07-23 12:26                   ` Rik van Riel
2018-07-24 16:33               ` Will Deacon
     [not found]             ` <CF849A07-B7CE-4DE9-8246-53AC5A53A705@surriel.com>
2018-07-19 17:18               ` Andy Lutomirski
2018-07-20  8:02             ` Vitaly Kuznetsov
2018-07-20  9:49               ` Peter Zijlstra
2018-07-20 10:18                 ` Vitaly Kuznetsov [this message]
2018-07-20  9:32             ` Peter Zijlstra
2018-07-20 11:04               ` Peter Zijlstra
2018-07-16 19:03 ` [PATCH 5/7] x86,tlb: only send page table free TLB flush to lazy TLB CPUs Rik van Riel
2018-07-17  9:35   ` [tip:x86/mm] x86/mm/tlb: Only " tip-bot for Rik van Riel
2018-07-17 11:39     ` Peter Zijlstra
     [not found]       ` <1F8BDD25-864D-4105-B872-2109AA417454@surriel.com>
     [not found]         ` <24AA4367-22A1-450E-8F6A-3CBF39518384@surriel.com>
2018-07-18 16:19           ` Peter Zijlstra
2018-07-16 19:03 ` [PATCH 6/7] x86,mm: always use lazy TLB mode Rik van Riel
2018-07-17  9:36   ` [tip:x86/mm] x86/mm/tlb: Always " tip-bot for Rik van Riel
2018-10-09 14:58   ` tip-bot for Rik van Riel
2018-07-16 19:03 ` [PATCH 7/7] x86,switch_mm: skip atomic operations for init_mm Rik van Riel
2018-07-17  9:36   ` [tip:x86/mm] x86/mm/tlb: Skip atomic operations for 'init_mm' in switch_mm_irqs_off() tip-bot for Rik van Riel
  -- strict thread matches above, loose matches on Subject: below --
2018-07-10 14:28 [PATCH v5 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-10 14:28 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-07-06 21:56 [PATCH v4 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-06 21:56 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-06-29 14:29 [PATCH v3 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-06-29 14:29 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-06-29 17:05   ` Dave Hansen
2018-06-29 17:29     ` Rik van Riel
2018-06-20 19:56 [PATCH 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-06-20 19:56 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-06-22 15:04   ` Andy Lutomirski
2018-06-22 15:15     ` Rik van Riel
2018-06-22 15:34       ` Andy Lutomirski
2018-06-22 17:05   ` Dave Hansen
2018-06-22 17:16     ` Rik van Riel

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