On Tue, May 14, 2019 at 02:34:10PM -0700, Eric Biggers wrote: > On Tue, May 14, 2019 at 06:33:48PM +0200, David Sterba wrote: > > Hi, > > > > Q: is there a way to query the crypto layer whether a given algorithm > > (digest, crypto) is accelerated by the driver? > > > > This information can be used to decide if eg. a checksum should can be > > calculated right away or offloaded to a thread. This is done in btrfs, > > (fs/btrfs/disk-io.c:check_async_write). > > > > At this moment it contains a static check for a cpu feature, and only > > for x86. I briefly searched the arch/ directory for implementations of > > crc32c that possibly use hw aid and there are several of them. Adding a > > static check a-la x86 for the other architectures (arm, ppc, mips, > > sparc, s390) is wrong, so I'm looking for a clean solution. > > > > The struct shash_alg definition of the algorithms does not say anything > > about the acceleration. The closest thing is the cra_priority, but I > > don't know if this is reliable information. The default implementations > > seem to have 100, and acceleated 200 or 300. > > > > This would be probably sufficient, but I'd like a confirmation from > > crypto people. > > > > There's only one default implementation of crc32c, not multiple, and it has > priority 100. All other crc32c implementations have priority > 100. So yes, > you can check the priority (which would require adding a function to > lib/libcrc32c.c to get it). Alternatively you could check whether the driver > name is "crc32c-generic" or not. Thanks, the driver name check seems to be ok for my needs. At mount time the struct crypto_shash is initialized and this provides the driver name, then a bit is set whether it's generic or not and later used to decide whether to offload.
