On Thu, Jan 07, 2021 at 02:27:51PM -0800, Eric Biggers wrote: > On Thu, Jan 07, 2021 at 10:48:05PM +0100, Arnd Bergmann wrote: > > On Thu, Jan 7, 2021 at 5:27 PM Theodore Ts'o <tytso@xxxxxxx> wrote: > > > > > > On Thu, Jan 07, 2021 at 01:37:47PM +0000, Russell King - ARM Linux admin wrote: > > > > > The gcc bugzilla mentions backports into gcc-linaro, but I do not see > > > > > them in my git history. > > > > > > > > So, do we raise the minimum gcc version for the kernel as a whole to 5.1 > > > > or just for aarch64? > > > > > > Russell, Arnd, thanks so much for tracking down the root cause of the > > > bug! > > > > There is one more thing that I wondered about when looking through > > the ext4 code: Should it just call the crc32c_le() function directly > > instead of going through the crypto layer? It seems that with Ard's > > rework from 2018, that can just call the underlying architecture specific > > implementation anyway. > > > > It looks like that would work, although note that crc32c_le() uses the shash API > too, so it isn't any more "direct" than what ext4 does now. Yes. > Also, a potential issue is that the implementation of crc32c that crc32c_le() > uses might be chosen too early if the architecture-specific implementation of > crc32c is compiled as a module (e.g. crc32c-intel.ko). This was the primary reason I chose to do it this way for ext4. The other is that ext4 didn't use crc32c before metadata_csum, so there's no point in pulling in the crypto layer if you're only going to use older ext2 or ext3 filesystems. That was 2010, maybe people have stopped doing that? > There are two ways this > could be fixed -- either by making it a proper library API like blake2s() that > can call the architecture-specific code directly, or by reconfiguring things > when a new crypto module is loaded (like what lib/crc-t10dif.c does). Though I would like to see the library functions gain the ability to use whatever is the fastest mechanism available once we can be reasonably certain that all the platform-specific drivers have been loaded. That said, IIRC most distros compile all of them into their (increasingly large) vmlinuz files so maybe this isn't much of practical concern? --D > > Until one of those is done, switching to crc32c_le() might cause performance > regressions. > > - Eric
