This is a follow up from the long-forgotten [1], but with some more convincing evidence. Consider the following script: #!/bin/bash -e # create 4G ramdisk sudo modprobe brd rd_nr=1 rd_size=4194304 # create a dm-crypt device with NULL cipher on top of /dev/ram0 echo '0 8388608 crypt capi:ecb(cipher_null) - 0 /dev/ram0 0' | sudo dmsetup create eram0 # create a dm-crypt device with NULL cipher and custom force_inline flag echo '0 8388608 crypt capi:ecb(cipher_null) - 0 /dev/ram0 0 1 force_inline' | sudo dmsetup create inline-eram0 # read all data from /dev/ram0 sudo dd if=/dev/ram0 bs=4k iflag=direct | sha256sum # read the same data from /dev/mapper/eram0 sudo dd if=/dev/mapper/eram0 bs=4k iflag=direct | sha256sum # read the same data from /dev/mapper/inline-eram0 sudo dd if=/dev/mapper/inline-eram0 bs=4k iflag=direct | sha256sum This script creates a ramdisk (to eliminate hardware bias in the benchmark) and two dm-crypt instances on top. Both dm-crypt instances use the NULL cipher to eliminate potentially expensive crypto bias (the NULL cipher just uses memcpy for "encyption"). The first instance is the current dm-crypt implementation from 5.8-rc1, the second is the dm-crypt instance with a custom new flag enabled from the patch attached to this thread. On my VM (Debian in VirtualBox with 4 cores on 2.8 GHz Quad-Core Intel Core i7) I get the following output (formatted for better readability): # plain ram0 1048576+0 records in 1048576+0 records out 4294967296 bytes (4.3 GB, 4.0 GiB) copied, 21.2305 s, 202 MB/s 8479e43911dc45e89f934fe48d01297e16f51d17aa561d4d1c216b1ae0fcddca - # eram0 (current dm-crypt) 1048576+0 records in 1048576+0 records out 4294967296 bytes (4.3 GB, 4.0 GiB) copied, 53.2212 s, 80.7 MB/s 8479e43911dc45e89f934fe48d01297e16f51d17aa561d4d1c216b1ae0fcddca - # inline-eram0 (patched dm-crypt) 1048576+0 records in 1048576+0 records out 4294967296 bytes (4.3 GB, 4.0 GiB) copied, 21.3472 s, 201 MB/s 8479e43911dc45e89f934fe48d01297e16f51d17aa561d4d1c216b1ae0fcddca - As we can see, current dm-crypt implementation creates a significant IO performance overhead (at least on small IO block sizes) for both latency and throughput. We suspect offloading IO request processing into workqueues and async threads is more harmful these days with the modern fast storage. I also did some digging into the dm-crypt git history and much of this async processing is not needed anymore, because the reasons it was added are mostly gone from the kernel. More details can be found in [2] (see "Git archeology" section). We have been running the attached patch on different hardware generations in more than 200 datacentres on both SATA SSDs and NVME SSDs and so far were very happy with the performance benefits. [1]: https://www.spinics.net/lists/dm-crypt/msg07516.html [2]: https://blog.cloudflare.com/speeding-up-linux-disk-encryption/ Ignat Korchagin (1): Add DM_CRYPT_FORCE_INLINE flag to dm-crypt target drivers/md/dm-crypt.c | 55 +++++++++++++++++++++++++++++++++---------- 1 file changed, 43 insertions(+), 12 deletions(-) -- 2.20.1 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
