From: Peter Zijlstra <peterz@infradead.org>
To: songliubraving@fb.com, linux-kernel@vger.kernel.org,
dave.hansen@intel.com, hpa@zytor.com, riel@surriel.com,
tglx@linutronix.de, mingo@kernel.org,
torvalds@linux-foundation.org
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/mm] x86/mm/tlb: Make lazy TLB mode lazier
Date: Tue, 17 Jul 2018 13:33:30 +0200 [thread overview]
Message-ID: <20180717113330.GU2476@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <tip-ac0315896970d8589291e9d8a1569fc65967b7f1@git.kernel.org>
On Tue, Jul 17, 2018 at 02:35:08AM -0700, tip-bot for Rik van Riel wrote:
> @@ -242,17 +244,40 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
> next->context.ctx_id);
>
> /*
> + * Even in lazy TLB mode, the CPU should stay set in the
> + * mm_cpumask. The TLB shootdown code can figure out from
> + * from cpu_tlbstate.is_lazy whether or not to send an IPI.
> */
> if (WARN_ON_ONCE(real_prev != &init_mm &&
> !cpumask_test_cpu(cpu, mm_cpumask(next))))
> cpumask_set_cpu(cpu, mm_cpumask(next));
>
> + /*
> + * If the CPU is not in lazy TLB mode, we are just switching
> + * from one thread in a process to another thread in the same
> + * process. No TLB flush required.
> + */
> + if (!was_lazy)
> + return;
> +
> + /*
> + * Read the tlb_gen to check whether a flush is needed.
> + * If the TLB is up to date, just use it.
> + * The barrier synchronizes with the tlb_gen increment in
> + * the TLB shootdown code.
> + */
> + smp_mb();
What exactly is this smp_mb() ordering? The above comment is
insufficient. Is it the cpumask_set_cpu() vs the atomic64_read() ?
If so, should this not be smp_mb__after_atomic() (iow a NO-OP on x86)
If it is not so, please fix the comment to explain things.
> + next_tlb_gen = atomic64_read(&next->context.tlb_gen);
> + if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) ==
> + next_tlb_gen)
> + return;
> +
> + /*
> + * TLB contents went out of date while we were in lazy
> + * mode. Fall through to the TLB switching code below.
> + */
> + new_asid = prev_asid;
> + need_flush = true;
next prev parent reply other threads:[~2018-07-17 11:33 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 [this message]
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
2018-07-20 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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