Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20221006223151.22159-1-elliott@hpe.com> <20221012215931.3896-1-elliott@hpe.com>
 <20221012215931.3896-10-elliott@hpe.com> <Y0ddUkGg15kHCIiB@zx2c4.com> <MW5PR84MB18427894BEF615BD08F4603EAB259@MW5PR84MB1842.NAMPRD84.PROD.OUTLOOK.COM>
In-Reply-To: <MW5PR84MB18427894BEF615BD08F4603EAB259@MW5PR84MB1842.NAMPRD84.PROD.OUTLOOK.COM>
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Thu, 13 Oct 2022 19:26:47 -0600
Message-ID: <CAHmME9p7SQv=iay3QujFU7jGaNXmhYhU9TWPobERBXQ1xNVV5g@mail.gmail.com>
Subject: Re: [PATCH v2 09/19] crypto: x86 - use common macro for FPU limit
To:     "Elliott, Robert (Servers)" <elliott@hpe.com>
Cc:     "herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
        "ap420073@gmail.com" <ap420073@gmail.com>,
        "ardb@kernel.org" <ardb@kernel.org>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Oct 13, 2022 at 3:48 PM Elliott, Robert (Servers)
<elliott@hpe.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.