[dm-devel] Slow write speeds on new laptop

[Matthew Wilcox]

I just got a Tiger Lake based laptop and installed Debian on it with
dm-crypt.  The installer attempts to write zeroes to the encrypted partition
in order to prevent various metadata attacks (using blockdev-wipe [1])

After about eight hours with it not even halfway, I aborted this attempt.
The drive is about a terabyte in size, so that's around 15MB/s.  This
is atrocious!  cryptsetup benchmark says the CPU is capable of doing
4GB/s with aes-xts and a 512b key.  The cipher in use is reported as
aes-xts-plain64.

dd iflag=direct of=/dev/null bs=64k count=100000 gives some pretty poor
results.  with if=/dev/nvme0n1p3, I get 1.2GB/s.  with if=/dev/dm-0,
I get 600MB/s.

I found this critique of the dm-crypt architecture:
https://blog.cloudflare.com/speeding-up-linux-disk-encryption/
I'm using Linux 5.9, and I'm not sure how much of this has been incorporated.

[1] https://salsa.debian.org/installer-team/partman-crypto/-/blob/master/blockdev-wipe/blockdev-wipe.c