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To: Nicholas Piggin <npiggin@gmail.com>, linuxppc-dev@lists.ozlabs.org
From: Michael Ellerman <patch-notifications@ellerman.id.au>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
 Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [v4, 1/7] powerpc/64s/radix: do not flush TLB when relaxing access
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Date: Tue,  5 Jun 2018 00:11:31 +1000 (AEST)
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On Fri, 2018-06-01 at 10:01:15 UTC, Nicholas Piggin wrote:
> Radix flushes the TLB when updating ptes to increase permissiveness
> of protection (increase access authority). Book3S does not require
> TLB flushing in this case, and it is not done on hash. This patch
> avoids the flush for radix.
> 
> >From Power ISA v3.0B, p.1090:
> 
>     Setting a Reference or Change Bit or Upgrading Access Authority
>     (PTE Subject to Atomic Hardware Updates)
> 
>     If the only change being made to a valid PTE that is subject to
>     atomic hardware updates is to set the Reference or Change bit to 1
>     or to add access authorities, a simpler sequence suffices because
>     the translation hardware will refetch the PTE if an access is
>     attempted for which the only problems were reference and/or change
>     bits needing to be set or insufficient access authority.
> 
> The nest MMU on POWER9 does not re-fetch the PTE after such an access
> attempt before faulting, so address spaces with a coprocessor
> attached will continue to flush in these cases.
> 
> This reduces tlbies for a kernel compile workload from 1.28M to 0.95M,
> tlbiels from 20.17M 19.68M.
> 
> fork --fork --exec benchmark improved 2.77% (12000->12300).
> 
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/e5f7cb58c2b77a0249c2028b6d1ec4

cheers