From: Peter Zijlstra <peterz@infradead.org>
To: Rik van Riel <riel@surriel.com>
Cc: songliubraving@fb.com, linux-kernel@vger.kernel.org,
dave.hansen@intel.com, hpa@zytor.com, tglx@linutronix.de,
mingo@kernel.org, torvalds@linux-foundation.org,
linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/mm] x86/mm/tlb: Make lazy TLB mode lazier
Date: Wed, 18 Jul 2018 18:00:07 +0200 [thread overview]
Message-ID: <20180718160007.GS2494@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <08AC2AF2-17DE-4416-BBBD-B6B950D20906@surriel.com>
On Wed, Jul 18, 2018 at 11:33:02AM -0400, Rik van Riel wrote:
> The tlb flush code first increments mm->context.tlb_gen, and then sends
> shootdown IPIs to CPUs that have this mm loaded and are not in lazy
> TLB mode.
>
> At context switch time, we have to ensure that we check the tlb_gen after
> we load the old is_lazy state.
>
> Maybe something like this?
>
> /*
> * Read the tlb_gen to check whether a flush is needed.
> * If the TLB is up to date, just use it.
> * The TLB shootdown code first increments tlb_gen, and then
> * sends IPIs to CPUs that have this CPU loaded and are not
> * in lazy TLB mode. The barrier ensures we handle
> * cpu_tlbstate.is_lazy before tlb_gen, keeping this code
> * synchronized with the TLB flush code.
> */
Let me try and draw a diagram; that always works better for me that
text. So the relevant ordering is something like:
CPU0 - switch_mm() CPU1 - flush_tlb_mm_range()
[W] cpu_tlbstate.is_lazy = false; [RmW] next->tlb_gen++
smp_mb() MB (implied)
[R] tlb_gen = next->tlb_gen native_flush_tlb_others()
[R] cpu_tlbstate.is_lazy
Such that CPU1 either observes !lazy and flushes and/or CPU0 observes
the generation increment and forces a flush itself.
Either way, CPU0 gets flushed.
Also, I don't suppose you've looked at the paravirt instances of
flush_tlb_other() ? They don't elide the flushes because of lazy.
next prev parent reply other threads:[~2018-07-18 16:00 UTC|newest]
Thread overview: 49+ 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 [this message]
[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
2018-07-20 4:57 ` Benjamin Herrenschmidt
2018-07-20 8:30 ` Peter Zijlstra
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
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
2018-09-26 3:58 [PATCH 7/7] x86/mm/tlb: Make lazy TLB mode lazier Rik van Riel
2018-10-09 15:01 ` [tip:x86/mm] " tip-bot for Rik van Riel
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