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

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Date:   Wed, 12 Jul 2023 08:08:42 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     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

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?).
> 
> 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.

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