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From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: aneesh.kumar@linux.vnet.ibm.com, akpm@linux-foundation.org,
	npiggin@gmail.com, linux-arch@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux@armlinux.org.uk, heiko.carstens@de.ibm.com,
	riel@surriel.com
Subject: Re: [PATCH v6 05/18] asm-generic/tlb: Provide generic tlb_flush() based on flush_tlb_mm()
Date: Tue, 19 Feb 2019 12:47:16 +0000
Message-ID: <20190219124716.GB8501@fuggles.cambridge.arm.com> (raw)
In-Reply-To: <20190219103233.148854086@infradead.org>

On Tue, Feb 19, 2019 at 11:31:53AM +0100, Peter Zijlstra wrote:
> When an architecture does not have (an efficient) flush_tlb_range(),
> but instead always uses full TLB invalidates, the current generic
> tlb_flush() is sub-optimal, for it will generate extra flushes in
> order to keep the range small.
> 
> But if we cannot do range flushes, that is a moot concern. Optionally
> provide this simplified default.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  include/asm-generic/tlb.h |   41 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
> 
> --- a/include/asm-generic/tlb.h
> +++ b/include/asm-generic/tlb.h
> @@ -114,7 +114,8 @@
>   *    returns the smallest TLB entry size unmapped in this range.
>   *
>   * If an architecture does not provide tlb_flush() a default implementation
> - * based on flush_tlb_range() will be used.
> + * based on flush_tlb_range() will be used, unless MMU_GATHER_NO_RANGE is
> + * specified, in which case we'll default to flush_tlb_mm().
>   *
>   * Additionally there are a few opt-in features:
>   *
> @@ -140,6 +141,9 @@
>   *  the page-table pages. Required if you use HAVE_RCU_TABLE_FREE and your
>   *  architecture uses the Linux page-tables natively.
>   *
> + *  MMU_GATHER_NO_RANGE
> + *
> + *  Use this if your architecture lacks an efficient flush_tlb_range().
>   */
>  #define HAVE_GENERIC_MMU_GATHER
>  
> @@ -302,12 +306,45 @@ static inline void __tlb_reset_range(str
>  	 */
>  }
>  
> +#ifdef CONFIG_MMU_GATHER_NO_RANGE
> +
> +#if defined(tlb_flush) || defined(tlb_start_vma) || defined(tlb_end_vma)
> +#error MMU_GATHER_NO_RANGE relies on default tlb_flush(), tlb_start_vma() and tlb_end_vma()
> +#endif
> +
> +/*
> + * When an architecture does not have efficient means of range flushing TLBs
> + * there is no point in doing intermediate flushes on tlb_end_vma() to keep the
> + * range small. We equally don't have to worry about page granularity or other
> + * things.
> + *
> + * All we need to do is issue a full flush for any !0 range.
> + */
> +static inline void tlb_flush(struct mmu_gather *tlb)
> +{
> +	if (tlb->end)
> +		flush_tlb_mm(tlb->mm);
> +}

I guess another way we could handle these architectures is by
unconditionally resetting tlb->fullmm to 1, but this works too.

Acked-by: Will Deacon <will.deacon@arm.com>

Will


  reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-19 10:31 [PATCH v6 00/18] generic mmu_gather patches Peter Zijlstra
2019-02-19 10:31 ` [PATCH v6 01/18] asm-generic/tlb: Provide a comment Peter Zijlstra
2019-02-19 10:31 ` [PATCH v6 02/18] asm-generic/tlb: Provide HAVE_MMU_GATHER_PAGE_SIZE Peter Zijlstra
2019-02-19 10:31 ` [PATCH v6 03/18] asm-generic/tlb: Provide generic VIPT cache flush Peter Zijlstra
2019-02-19 10:31 ` [PATCH v6 04/18] asm-generic/tlb: Provide generic tlb_flush() based on flush_tlb_range() Peter Zijlstra
2019-02-19 10:31 ` [PATCH v6 05/18] asm-generic/tlb: Provide generic tlb_flush() based on flush_tlb_mm() Peter Zijlstra
2019-02-19 12:47   ` Will Deacon [this message]
2019-02-19 10:31 ` [PATCH v6 06/18] asm-generic/tlb: Conditionally provide tlb_migrate_finish() Peter Zijlstra
2019-02-19 12:47   ` Will Deacon
2019-02-19 13:41     ` Peter Zijlstra
2019-02-20 14:47       ` Will Deacon
2019-02-20 15:02         ` Matthew Wilcox
2019-02-19 10:31 ` [PATCH v6 07/18] asm-generic/tlb: Invert HAVE_RCU_TABLE_INVALIDATE Peter Zijlstra
2019-02-19 10:31 ` [PATCH v6 08/18] arm/tlb: Convert to generic mmu_gather Peter Zijlstra
2019-02-19 10:31 ` [PATCH v6 09/18] ia64/tlb: Conver " Peter Zijlstra
2019-02-19 12:47   ` Will Deacon
2019-02-21  2:52   ` Souptick Joarder
2019-02-19 10:31 ` [PATCH v6 10/18] sh/tlb: Convert SH " Peter Zijlstra
2019-12-03 11:19   ` Geert Uytterhoeven
2019-12-04 10:47     ` Peter Zijlstra
2019-12-04 12:32       ` Geert Uytterhoeven
2019-12-04 13:22         ` Guenter Roeck
2019-12-04 15:17           ` Geert Uytterhoeven
2019-12-04 19:03             ` Guenter Roeck
2019-12-04 13:34         ` Peter Zijlstra
2019-12-04 15:07           ` Geert Uytterhoeven
2019-12-04 16:41             ` Peter Zijlstra
2019-12-05 15:26               ` Geert Uytterhoeven
2019-12-05 19:24       ` Rob Landley
2019-12-05 19:23         ` Rich Felker
2019-12-05 19:30       ` John Paul Adrian Glaubitz
2019-12-05 22:56         ` Guenter Roeck
2019-12-06 13:38           ` John Paul Adrian Glaubitz
2019-12-06 14:03             ` Guenter Roeck
2019-02-19 10:31 ` [PATCH v6 11/18] um/tlb: Convert " Peter Zijlstra
2019-02-19 10:32 ` [PATCH v6 12/18] arch/tlb: Clean up simple architectures Peter Zijlstra
2019-02-19 10:32 ` [PATCH v6 13/18] asm-generic/tlb: Introduce HAVE_MMU_GATHER_NO_GATHER Peter Zijlstra
2019-02-19 12:47   ` Will Deacon
2019-02-19 10:32 ` [PATCH v6 14/18] s390/tlb: convert to generic mmu_gather Peter Zijlstra
2019-02-19 12:47   ` Will Deacon
2019-02-19 10:32 ` [PATCH v6 15/18] asm-generic/tlb: Remove arch_tlb*_mmu() Peter Zijlstra
2019-02-19 10:32 ` [PATCH v6 16/18] asm-generic/tlb: Remove HAVE_GENERIC_MMU_GATHER Peter Zijlstra
2019-02-19 10:32 ` [PATCH v6 17/18] asm-generic/tlb: Remove tlb_flush_mmu_free() Peter Zijlstra
2019-02-19 10:32 ` [PATCH v6 18/18] asm-generic/tlb: Remove tlb_table_flush() Peter Zijlstra

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