linux-kernel - Re: [PATCH 0/4] riscv: tlb flush improvements

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Date:   Wed, 12 Jul 2023 17:18:00 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Conor Dooley <conor.dooley@...rochip.com>,
        Alexandre Ghiti <alexghiti@...osinc.com>
Cc:     Will Deacon <will@...nel.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mayuresh Chitale <mchitale@...tanamicro.com>,
        Vincent Chen <vincent.chen@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] riscv: tlb flush improvements

Hi Conor,


On 12/07/2023 09:08, Conor Dooley wrote:
> Hey Alex,
>
> On Tue, Jul 11, 2023 at 09:54:30AM +0200, Alexandre Ghiti wrote:
>> This series optimizes the tlb flushes on riscv which used to simply
>> flush the whole tlb whatever the size of the range to flush or the size
>> of the stride.
>>
>> Patch 3 introduces a threshold that is microarchitecture specific and
>> will very likely be modified by vendors, not sure though which mechanism
>> we'll use to do that (dt? alternatives? vendor initialization code?).


@Conor any idea how to achieve this?


>>
>> Next steps would be to implement:
>> - svinval extension as Mayuresh did here [1]
>> - BATCHED_UNMAP_TLB_FLUSH (I'll wait for arm64 patchset to land)
>> - MMU_GATHER_RCU_TABLE_FREE
>> - MMU_GATHER_MERGE_VMAS
>>
>> Any other idea welcome.
>>
>> [1] https://lore.kernel.org/linux-riscv/20230623123849.1425805-1-mchitale@ventanamicro.com/
>>
>> Alexandre Ghiti (4):
>>    riscv: Improve flush_tlb()
>>    riscv: Improve flush_tlb_range() for hugetlb pages
>>    riscv: Make __flush_tlb_range() loop over pte instead of flushing the
>>      whole tlb
> The whole series does not build on nommu & this one adds a build warning
> for regular builds:
> +      1 ../arch/riscv/mm/tlbflush.c:32:15: warning: symbol 'tlb_flush_all_threshold' was not declared. Should it be static?
>
> Cheers,
> Conor.


I'll fix the nommu build, sorry about that. Weird I missed this warning, 
that's an LLVM build right? That variable will need to overwritten by 
the vendors, so that should not be static (but it will depend on what 
solution we implement).


Thanks,


Alex