-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi Community, I use an Atom 330 (Dual-Core) ION based system as work station at home. The rootfs is crypted with cryptsetup/luks. As the Atom 330 is rather weak in cryptographic speed and I realized that a single blockdevice is always handled by only one kcryptd thread, I tried out a tweak to spread the work to 2 CPU cores. I have a volume group on the built-in SSD of the Nettop and I created two equally-sized volumes. Each of the volumes is encrypted using cryptsetup. When both volumes are succesfully unlocked they form a raid-0 device. Since I work on an SSD this should not create a performance problem due to high amount of seeks. And here is what is totally strange: When I read from this raid, I get a throughput of about 24MB/s (what is about the amount an Atom Core @1.6GHz (aes_x86) can decrypt per second. Looking at the 2 kcryptd processes I find that each is using nearly 50% cpu time. As if they where running only on a single core and/or waiting for each other?! lieven@dozer64-ssd:~$ sh speedtest-read.sh Sa 1. Aug 21:52:19 CEST 2009 1024+0 Datensätze ein 1024+0 Datensätze aus 1073741824 Bytes (1,1 GB) kopiert, 43,661 s, 24,6 MB/s Sa 1. Aug 21:53:03 CEST 2009 # 1024MB / 44 sec = 23,2 MB/sec lieven@dozer64-ssd:~$ cat speedtest-read.sh #!/bin/sh sync date dd if=/home/lieven/speedtest.dat of=/dev/null bs=1M sync date hdparm outputs about the same performance: lieven@dozer64-ssd:~$ sudo hdparm -tT /dev/md0 /dev/md0: Timing cached reads: 1244 MB in 2.00 seconds = 621.48 MB/sec Timing buffered disk reads: 70 MB in 3.04 seconds = 23.01 MB/sec But, when I write to /dev/md0 I get a significantly better performance: lieven@dozer64-ssd:~$ sh speedtest-write.sh Sa 1. Aug 22:19:04 CEST 2009 1024+0 Datensätze ein 1024+0 Datensätze aus 1073741824 Bytes (1,1 GB) kopiert, 27,2655 s, 39,4 MB/s Sa 1. Aug 22:19:36 CEST 2009 # 1024 MB / 32 sec = 32 MB / sec lieven@dozer64-ssd:~$ cat speedtest-write.sh #!/bin/sh sync date dd if=/dev/zero of=/home/lieven/speedtest.dat bs=1M count=1024 sync date If I look at the both kcryptd processes I see that both are using roughly 100% of one CPU core each when i write to /dev/md0. Before I made this setup, I tried it on an unencrypted volume with 2 files mounted via loop, crypted and then added to raid. In this case, the read performance is as expected (about 45MB/s). I tried with ubuntu jaunty kernel 2.6.28-13 and I also tried 2.6.30.4 as I read about the kcrypt workqueue patch that was added recently. Does anyone have an explaination for this? Thanks, Peter -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkp3PVMACgkQO/ibohXUOnKYXQCcDrZ0qmnfsn+IkBoAmnEZXkVN rWAAoL0NYiPYeawhMMP2zvbslftyhNeZ =IfDQ -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
