From: Jeff Law <jlaw@ventanamicro.com>
To: linux-riscv@lists.infradead.org
Subject: Re: [PATCH v3 0/6] RISC-V: Apply Zicboz to clear_page
Date: Mon, 30 Jan 2023 11:30:38 -0700 [thread overview]
Message-ID: <e9990765-9df9-70f5-cc85-32773b35710c@ventanamicro.com> (raw)
In-Reply-To: <20230130120128.1349464-1-ajones@ventanamicro.com>
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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next prev parent reply other threads:[~2023-01-30 18:31 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 ` Jeff Law [this message]
2023-01-30 18:47 ` [PATCH v3 0/6] RISC-V: Apply Zicboz to clear_page Andrew Jones
2023-01-30 18:55 ` Jeff Law
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