Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     Jeffrey Lien <Jeff.Lien@wdc.com>,
        Christoph Hellwig <hch@infradead.org>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-crypto\@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "linux-block\@vger.kernel.org" <linux-block@vger.kernel.org>,
        "linux-scsi\@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        "herbert\@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
        "tim.c.chen\@linux.intel.com" <tim.c.chen@linux.intel.com>,
        David Darrington <david.darrington@wdc.com>,
        Jeff Furlong <jeff.furlong@wdc.com>
Subject: Re: [PATCH] Performance Improvement in CRC16 Calculations.
From:   "Martin K. Petersen" <martin.petersen@oracle.com>
Organization: Oracle Corporation
References: <1533928331-21303-1-git-send-email-jeff.lien@wdc.com>
        <yq1in4gq5jf.fsf@oracle.com> <yq1lg8zb2lp.fsf@oracle.com>
        <20180822062016.GA10356@infradead.org>
        <SN1PR04MB18241CBDC8E4CA5275EE4424EA360@SN1PR04MB1824.namprd04.prod.outlook.com>
        <CAKv+Gu-RwCrdgW69NVpyRLwGPGPCZx+ksTBM7NZk7v0-dzczGg@mail.gmail.com>
Date:   Fri, 24 Aug 2018 12:29:25 -0400
In-Reply-To: <CAKv+Gu-RwCrdgW69NVpyRLwGPGPCZx+ksTBM7NZk7v0-dzczGg@mail.gmail.com>
        (Ard Biesheuvel's message of "Fri, 24 Aug 2018 16:39:47 +0100")
Message-ID: <yq1a7pb9196.fsf@oracle.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


Ard,

> Would it be possible to allocate the crypto transform upon first use
> instead of from an initcall? If crc_t10dif() is mostly called from
> non-process context, that would not really work, but otherwise, we
> could simply defer it (and occasional calls from non-process context
> that do occur would use the generic code until the point where another
> call from process context allocates the transform)

The function is always called from user context. However, postponing the
crypto transform registration doesn't solve the common scenario of the
user booting off of a Fibre Channel/SAS/NVMe device with the desired
crct10dif-pclmul.ko module located on the boot drive.

If there is no good way to teach crypto to update existing registrations
when a higher priority transformation becomes available, then we
probably need to explore tweaking dracut to unconditionally load
crct10dif-pclmul (and your ARM equivalent). Looks like there are already
hacks in place in dracut to preload crc32c for btrfs and XFS.

Anyway. Just seems like the kernel is violating the principle of least
surprise here. The kernel should always pick the best available tool for
the job...

-- 
Martin K. Petersen	Oracle Linux Engineering