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From: Andrew Morton <akpm@linux-foundation.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: peterz@infradead.org, will@kernel.org, mpe@ellerman.id.au,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v4 3/9] asm-generic/tlb: Avoid potential double flush
Date: Thu, 16 Jan 2020 17:46:26 -0800	[thread overview]
Message-ID: <20200116174626.0244f71bbff64eee6c7faa1d@linux-foundation.org> (raw)
In-Reply-To: <c12bb139-9eda-74a9-b4de-b147a88ed1b0@linux.ibm.com>

On Thu, 16 Jan 2020 12:19:59 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> wrote:

> On 1/16/20 12:15 PM, Aneesh Kumar K.V wrote:
> > From: Peter Zijlstra <peterz@infradead.org>
> > 
> > Aneesh reported that:
> > 
> > 	tlb_flush_mmu()
> > 	  tlb_flush_mmu_tlbonly()
> > 	    tlb_flush()			<-- #1
> > 	  tlb_flush_mmu_free()
> > 	    tlb_table_flush()
> > 	      tlb_table_invalidate()
> > 		tlb_flush_mmu_tlbonly()
> > 		  tlb_flush()		<-- #2
> > 
> > does two TLBIs when tlb->fullmm, because __tlb_reset_range() will not
> > clear tlb->end in that case.
> > 
> > Observe that any caller to __tlb_adjust_range() also sets at least one
> > of the tlb->freed_tables || tlb->cleared_p* bits, and those are
> > unconditionally cleared by __tlb_reset_range().
> > 
> > Change the condition for actually issuing TLBI to having one of those
> > bits set, as opposed to having tlb->end != 0.
> > 
> 
> 
> We should possibly get this to stable too along with the first two 
> patches. I am not quiet sure if this will qualify for a stable backport. 
> Hence avoided adding Cc:stable@kernel.org

I'm not seeing any description of the user-visible runtime effects. 
Always needed, especially for -stable, please.

It appears to be a small performance benefit?  If that benefit was
"large" and measurements were presented then that would be something
we might wish to backport.



  reply	other threads:[~2020-01-17  1:46 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16  6:45 [PATCH v4 0/9] Fixup page directory freeing Aneesh Kumar K.V
2020-01-16  6:45 ` [PATCH v4 1/9] powerpc/mmu_gather: Enable RCU_TABLE_FREE even for !SMP case Aneesh Kumar K.V
2020-01-18 11:01   ` Michael Ellerman
2020-01-16  6:45 ` [PATCH v4 2/9] mm/mmu_gather: Invalidate TLB correctly on batch allocation failure and flush Aneesh Kumar K.V
2020-01-18 11:04   ` Michael Ellerman
2020-01-16  6:45 ` [PATCH v4 3/9] asm-generic/tlb: Avoid potential double flush Aneesh Kumar K.V
2020-01-16  6:49   ` Aneesh Kumar K.V
2020-01-17  1:46     ` Andrew Morton [this message]
2020-01-16  6:45 ` [PATCH v4 4/9] asm-gemeric/tlb: Remove stray function declarations Aneesh Kumar K.V
2020-01-16  6:45 ` [PATCH v4 5/9] asm-generic/tlb: Add missing CONFIG symbol Aneesh Kumar K.V
2020-01-16  6:45 ` [PATCH v4 6/9] asm-generic/tlb: Rename HAVE_RCU_TABLE_FREE Aneesh Kumar K.V
2020-01-18  5:56   ` Aneesh Kumar K.V
2020-01-16  6:45 ` [PATCH v4 7/9] asm-generic/tlb: Rename HAVE_MMU_GATHER_PAGE_SIZE Aneesh Kumar K.V
2020-01-16  6:45 ` [PATCH v4 8/9] asm-generic/tlb: Rename HAVE_MMU_GATHER_NO_GATHER Aneesh Kumar K.V
2020-01-16  6:45 ` [PATCH v4 9/9] asm-generic/tlb: Provide MMU_GATHER_TABLE_FREE Aneesh Kumar K.V

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