From: Ard Biesheuvel Subject: Re: [PATCH] Performance Improvement in CRC16 Calculations. Date: Fri, 24 Aug 2018 16:39:47 +0100 Message-ID: References: <1533928331-21303-1-git-send-email-jeff.lien@wdc.com> <20180822062016.GA10356@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: Christoph Hellwig , "Martin K. Petersen" , "linux-kernel@vger.kernel.org" , "linux-crypto@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "herbert@gondor.apana.org.au" , "tim.c.chen@linux.intel.com" , David Darrington , Jeff Furlong To: Jeffrey Lien Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On 24 August 2018 at 16:32, Jeffrey Lien 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 > Cc: Jeffrey Lien ; 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 ; Jeff Furlong > Subject: Re: [PATCH] Performance Improvement in CRC16 Calculations. > > On Tue, Aug 21, 2018 at 09:40:34PM -0400, Martin K. Petersen wrote: >> 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. > >> 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.