linux-kernel - Re: [PATCH v2 09/19] crypto: x86 - use common macro for FPU limit

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Date:   Thu, 13 Oct 2022 19:26:47 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     "Elliott, Robert (Servers)" <elliott@....com>
Cc:     "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "ap420073@...il.com" <ap420073@...il.com>,
        "ardb@...nel.org" <ardb@...nel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 09/19] crypto: x86 - use common macro for FPU limit

On Thu, Oct 13, 2022 at 3:48 PM Elliott, Robert (Servers)
<elliott@....com> wrote:
> Perhaps we should declare a time goal like "30 us," measure the actual
> speed of each algorithm with a tcrypt speed test, and calculate the
> nominal value assuming some slow x86 CPU core speed?

Sure, pick something reasonable with good margin for a reasonable CPU.
It doesn't have to be perfect, but just vaguely right for supported
hardware.

> That could be further adjusted at run-time based on the supposed
> minimum CPU frequency (e.g., as reported in
> /sys/devices/system/cpu/cpufreq/policy0/scaling_min_freq).

Oh no, please no. Not another runtime knob. That also will make the
loop less efficient.