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From: Jeff Law <jlaw@ventanamicro.com>
To: Andrew Jones <ajones@ventanamicro.com>,
	linux-riscv@lists.infradead.org, kvm-riscv@lists.infradead.org,
	devicetree@vger.kernel.org
Cc: 'Heiko Stuebner ' <heiko@sntech.de>,
	'Krzysztof Kozlowski ' <krzysztof.kozlowski+dt@linaro.org>,
	'Anup Patel ' <apatel@ventanamicro.com>,
	'Palmer Dabbelt ' <palmer@dabbelt.com>,
	'Atish Patra ' <atishp@rivosinc.com>,
	'Paul Walmsley ' <paul.walmsley@sifive.com>,
	'Albert Ou ' <aou@eecs.berkeley.edu>,
	'Conor Dooley ' <conor.dooley@microchip.com>,
	'Rob Herring ' <robh@kernel.org>,
	'Jisheng Zhang ' <jszhang@kernel.org>
Subject: Re: [PATCH v3 0/6] RISC-V: Apply Zicboz to clear_page
Date: Mon, 30 Jan 2023 11:55:10 -0700	[thread overview]
Message-ID: <5afd356d-7ed6-6f14-49be-246ff43d233f@ventanamicro.com> (raw)
In-Reply-To: <20230130120128.1349464-1-ajones@ventanamicro.com>

[ Sorry for the duplicate.  Andrew indicated I'd used reply-list rather 
than reply-all.  ]


On 1/30/23 05:01, Andrew Jones wrote:
> When the Zicboz extension is available we can more rapidly zero naturally
> aligned Zicboz block sized chunks of memory. As pages are always page
> aligned and are larger than any Zicboz block size will be, then
> clear_page() appears to be a good candidate for the extension. While cycle
> count and energy consumption should also be considered, we can be pretty
> certain that implementing clear_page() with the Zicboz extension is a win
> by comparing the new dynamic instruction count with its current count[1].
> Doing so we see that the new count is just over a quarter of the old count
> (see patch4's commit message for more details).
> 
> For those of you who reviewed v1[2], you may be looking for the memset()
> patches. As pointed out in v1, and a couple follow-up emails, it's not
> clear that patching memset() is a win yet. When I get a chance to test
> on real hardware with a comprehensive benchmark collection then I can
> post the memset() patches separately (assuming the benchmarks show it's
> worthwhile).
> 
So a note.  On the userspace side we are using cboz for clearing memory 
in memset.  While the data is intermixed with other changes, there's a 
very significant drop in stores and a host of related low level 
performance counters and a notable uptick in gcc #5 performance from 
spec2017 which is particularly sensitive to memory clearing.  We haven't 
seen any performance regressions attributable to using cboz across 
spec2017's integer suite.

I believe our current threshold setting is to use cboz for chunks >= 128 
bytes.

Jeff

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      parent reply	other threads:[~2023-01-30 18:55 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-30 12:01 [PATCH v3 0/6] RISC-V: Apply Zicboz to clear_page Andrew Jones
2023-01-30 12:01 ` [PATCH v3 1/6] RISC-V: Factor out body of riscv_init_cbom_blocksize loop Andrew Jones
2023-01-30 12:01 ` [PATCH v3 2/6] dt-bindings: riscv: Document cboz-block-size Andrew Jones
2023-01-30 12:25   ` Conor Dooley
2023-01-30 22:57   ` Rob Herring
2023-01-30 12:01 ` [PATCH v3 3/6] RISC-V: Add Zicboz detection and block size parsing Andrew Jones
2023-01-30 12:01 ` [PATCH v3 4/6] RISC-V: Use Zicboz in clear_page when available Andrew Jones
2023-02-02  4:35   ` Palmer Dabbelt
2023-02-02  7:41     ` Andrew Jones
2023-01-30 12:01 ` [PATCH v3 5/6] RISC-V: KVM: Provide UAPI for Zicboz block size Andrew Jones
2023-01-30 12:01 ` [PATCH v3 6/6] RISC-V: KVM: Expose Zicboz to the guest Andrew Jones
2023-01-30 18:30 ` [PATCH v3 0/6] RISC-V: Apply Zicboz to clear_page Jeff Law
2023-01-30 18:47   ` Andrew Jones
2023-01-30 18:55 ` Jeff Law [this message]

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