On 24 August 2018 at 16:32, Jeffrey Lien [off-list ref] wrote:

I rebuilt my 4.18 kernel with CONFIG_CRYPTO_CRCT10DIF_PCLMUL=3Dy as Marti=

n recommended and got even better performance results vs the CRC Slice by 1=
6 changes.  Here's a summary of the results

FIO Sequential Write, 64K Block Size, Queue Depth 64
PCLMUL =3D y Kernel:        bw =3D 2237 MiB/s
Slice by 16 CRC Calc:      bw =3D 1964 MiB/s
Base Kernel:                     bw =3D   357 MiB/s

FIO Sequential Read, 64K Block Size, Queue Depth 64
PCLMUL =3D y Kernel:        bw =3D 3839 MiB/s
Slice by 16 CRC Calc:      bw =3D 2730  MiB/s
Base Kernel:                     bw =3D   797 MiB/s

So it seems the CONFIG_CRYPTO_CRCT10DIF_PCLMUL=3Dy provides the best perf=

ormance.  Are there any negative side effect to this config option?   If no=
t, does it make sense to recommend all the major distro's change their conf=
ig options to have CONFIG_CRYPTO_CRCT10DIF_PCLMUL=3Dy as the default option=
?

I think the way the library version of crc_t10dif() invokes the crypto
API should be revised.

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)

-----Original Message-----
From: Christoph Hellwig [mailto:hch@infradead.org]
Sent: Wednesday, August 22, 2018 1:20 AM
To: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Jeffrey Lien <redacted>; linux-kernel@vger.kernel.org; linux=

-crypto@vger.kernel.org; linux-block@vger.kernel.org; linux-scsi@vger.kerne=
l.org; herbert@gondor.apana.org.au; tim.c.chen@linux.intel.com; David Darri=
ngton [off-list ref]; Jeff Furlong [off-list ref]

Subject: Re: [PATCH] Performance Improvement in CRC16 Calculations.

On Tue, Aug 21, 2018 at 09:40:34PM -0400, Martin K. Petersen wrote:

quoted

When crc-t10dif is initialized, the crypto infrastructure will pick
the algorithm with the highest priority currently registered. Both
block and SCSI will cause crc-t10dif to be compiled as a built-in so
this selection happens very early.

Ouch.  This might actually happen in a lot of other users of the crypto f=

unctionality as well.

quoted

However, it seems like a bit of a deficiency in crypto that there is
no way to upgrade existing transformations if higher priority
algorithms become available. btrfs and a few others work around this
issue by not using the generic lib/ CRC functions (which defeats the
purpose of having these in the first place). Instead they are
registering their own transformation at a later time where any
accelerator modules are more likely to be loaded.

If we can't fix this in crypto (which doesn't seem that easy), we should =

at least clearly document the issue somewhere, and fix this in the t10pi co=
de by initializing crct10dif_tfm in a lazy fashion only once the fist block=
 device starts using it.