On Fri, Sep 18, 2009 at 02:22:18PM +0200, Christian Pernegger wrote: > > Yes. And that may be some s"synergetic" effect triggered by the > > slowness. At least that is one possible explanation. > > Agreed. > > > You could try this with a dummy-cipher that does not take encryption time. > > > > I have not tried this myself, but hit candidates are > > "ciper_null" and "ecb(ciper_null)". I have both (kernel > > 2.6.30.5) > > They're there all right, must have overlooked them. However I haven't > managed to construct a cipher spec that'll work with cryptsetup. Maybe > because it takes no key ... Possibly. I do not know how to do this either. > Various tunings of the host's page cache (under /proc/sys/vm/) to make > flushes less bursty didn't help much. A pity. Have you tried to set dirty_writeback_centisecs to something very low, e.g. 10? If I understand this correctly that would cause regular flushes to start after 1 sec. > In the meantime I've set up a dedicated kvm guest for these tests, > with one encrypted and one unencrypted scratch volume. Maybe some > systematic benchmarking will point somewhere. Good approach. You can also try different speed ciphers. 2fish should be faster than AES. > Seems a lot of people are having this problem, since ~2.6.24 at least, > and it seems to get worse the slower the CPUs are, the faster the > disks are. Chosing a faster cipher seems to help. That would be consistent with a backlog before the cipher step that eventually leads to an emergency flush. One possible solution would be to slow down writes before the buffer becomes full. However I don't think there are provisions for that in the kernel. Arno > Chris > _______________________________________________ > dm-crypt mailing list > dm-crypt@xxxxxxxx > http://www.saout.de/mailman/listinfo/dm-crypt > -- Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@xxxxxxxxxxx GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans If it's in the news, don't worry about it. The very definition of "news" is "something that hardly ever happens." -- Bruce Schneier _______________________________________________ dm-crypt mailing list dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
