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

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Message-ID: <OSBPR01MB2037A987CEFA28B326F063AB80139@OSBPR01MB2037.jpnprd01.prod.outlook.com>
Date:   Fri, 18 Mar 2022 06:34:24 +0000
From:   "tarumizu.kohei@...itsu.com" <tarumizu.kohei@...itsu.com>
To:     'Dave Hansen' <dave.hansen@...el.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 0/8] Add hardware prefetch control driver for arm64 and
 x86

> 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?

In addition to the sample benchmarks in the [Merit] section, we assume
that some workloads will benefit from tweaking prefetches. We expect that
users can find the best parameters by using an tunable I/F from userspace.

I will find out the specific workload which improves the performance.