From: Andrea Parri <parri.andrea@gmail.com>
To: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Andrew Morton <akpm@linux-foundation.org>,
Ved Shanbhogue <ved@rivosinc.com>, Matt Evans <mev@rivosinc.com>,
Dylan Jhong <dylan@andestech.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
linux-mm@kvack.org
Subject: Re: [PATCH RFC/RFT v2 4/4] riscv: Stop emitting preventive sfence.vma for new userspace mappings with Svvptc
Date: Thu, 1 Feb 2024 16:03:48 +0100 [thread overview]
Message-ID: <Zbuy1E7mz9Oui1Dl@andrea> (raw)
In-Reply-To: <20240131155929.169961-5-alexghiti@rivosinc.com>
On Wed, Jan 31, 2024 at 04:59:29PM +0100, Alexandre Ghiti wrote:
> The preventive sfence.vma were emitted because new mappings must be made
> visible to the page table walker but Svvptc guarantees that xRET act as
> a fence, so no need to sfence.vma for the uarchs that implement this
> extension.
AFAIU, your first submission shows that you don't need that xRET property.
Similarly for other archs. What was rationale behind this Svvptc change?
> This allows to drastically reduce the number of sfence.vma emitted:
>
> * Ubuntu boot to login:
> Before: ~630k sfence.vma
> After: ~200k sfence.vma
>
> * ltp - mmapstress01
> Before: ~45k
> After: ~6.3k
>
> * lmbench - lat_pagefault
> Before: ~665k
> After: 832 (!)
>
> * lmbench - lat_mmap
> Before: ~546k
> After: 718 (!)
This Svvptc seems to move/add the "burden" of the synchronization to xRET:
Perhaps integrate the above counts w/ the perf gains in the cover letter?
Andrea
next prev parent reply other threads:[~2024-02-01 15:04 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-31 15:59 [PATCH RFC v2 0/4] Svvptc extension to remove preventive sfence.vma Alexandre Ghiti
2024-01-31 15:59 ` [PATCH RFC/RFT v2 1/4] riscv: Add ISA extension parsing for Svvptc Alexandre Ghiti
2024-01-31 15:59 ` [PATCH RFC/RFT v2 2/4] dt-bindings: riscv: Add Svvptc ISA extension description Alexandre Ghiti
2024-02-01 9:22 ` Krzysztof Kozlowski
2024-01-31 15:59 ` [PATCH RFC/RFT v2 3/4] riscv: Stop emitting preventive sfence.vma for new vmalloc mappings Alexandre Ghiti
2024-06-03 2:26 ` [External] " yunhui cui
2024-06-03 12:02 ` Alexandre Ghiti
2024-06-04 6:21 ` yunhui cui
2024-06-04 7:15 ` Alexandre Ghiti
2024-06-04 7:17 ` Alexandre Ghiti
2024-06-04 8:51 ` Conor Dooley
2024-06-04 11:44 ` Alexandre Ghiti
2024-06-04 20:17 ` Conor Dooley
2024-01-31 15:59 ` [PATCH RFC/RFT v2 4/4] riscv: Stop emitting preventive sfence.vma for new userspace mappings with Svvptc Alexandre Ghiti
2024-02-01 15:03 ` Andrea Parri [this message]
2024-02-02 15:42 ` Alexandre Ghiti
2024-02-02 22:05 ` Alexandre Ghiti
2024-05-30 9:35 ` [External] " yunhui cui
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