linux-kernel - Re: [PATCH v2 0/8] Add hardware prefetch control driver for arm64 and x86

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Message-ID: <40b468cb-5144-77f0-963a-67e81d2e3aa4@intel.com>
Date:   Mon, 14 Mar 2022 12:19:21 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kohei Tarumizu <tarumizu.kohei@...itsu.com>,
        catalin.marinas@....com, will@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/8] Add hardware prefetch control driver for arm64 and
 x86

On 3/11/22 02:19, Kohei Tarumizu wrote:
> The advantage of using this is improved performance. As an example of
> performance improvements, the results of running the Stream benchmark
> on the A64FX are described in section [Merit].

I take it that there are users out there today that are sufficiently
motivated by the increased performance that they just do "wrmsr 0x1a4
0x1234".

You talked about this in the "[Merit]" section.  But, that's a _little_
unconvincing.  I don't doubt that there is *a* workload out there that
can benefit from hardware prefetcher tweaks.

Do we really expect end users to run their workloads and tweak these
values to find something optimal for them?