On 24 August 2018 at 16:32, Jeffrey Lien <jeff.l...@wdc.com> wrote: > I rebuilt my 4.18 kernel with CONFIG_CRYPTO_CRCT10DIF_PCLMUL=y as Martin > recommended and got even better performance results vs the CRC Slice by 16 > changes. Here's a summary of the results > > FIO Sequential Write, 64K Block Size, Queue Depth 64 > PCLMUL = y Kernel: bw = 2237 MiB/s > Slice by 16 CRC Calc: bw = 1964 MiB/s > Base Kernel: bw = 357 MiB/s > > FIO Sequential Read, 64K Block Size, Queue Depth 64 > PCLMUL = y Kernel: bw = 3839 MiB/s > Slice by 16 CRC Calc: bw = 2730 MiB/s > Base Kernel: bw = 797 MiB/s > > So it seems the CONFIG_CRYPTO_CRCT10DIF_PCLMUL=y provides the best > performance. Are there any negative side effect to this config option? If > not, does it make sense to recommend all the major distro's change their > config options to have CONFIG_CRYPTO_CRCT10DIF_PCLMUL=y 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:h...@infradead.org] > Sent: Wednesday, August 22, 2018 1:20 AM > To: Martin K. Petersen <martin.peter...@oracle.com> > Cc: Jeffrey Lien <jeff.l...@wdc.com>; linux-ker...@vger.kernel.org; > linux-crypto@vger.kernel.org; linux-bl...@vger.kernel.org; > linux-s...@vger.kernel.org; herb...@gondor.apana.org.au; > tim.c.c...@linux.intel.com; David Darrington <david.darring...@wdc.com>; Jeff > Furlong <jeff.furl...@wdc.com> > 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 > functionality 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 code by > initializing crct10dif_tfm in a lazy fashion only once the fist block device > starts using it.
