On Tue, 1 Jun 2010, Herbert Xu wrote: > On Mon, May 31, 2010 at 10:44:30PM -0400, Mikulas Patocka wrote: > > Questions: > > > > If you are optimizing it, > > > > 1) why don't you optimize it in such a way that if one CPU submits > > requests, the crypto work is spread among all the CPUs? Currently it > > spreads the work only if different CPUs submit it. > > Because the crypto layer already provides that functionality, > through pcrypt. By instantiating pcrypt for a given algorithm, > you can parallelise that algorithm across CPUs. And how can I use pcrypt for dm-crypt? After a quick look at pcrypt sources, it seems to be dependent on aead and not useable for general encryption algorithms at all. I tried cryptd --- in theory it should work by requesting the algorithm like cryptd(cbc(aes)) --- but if I replace "%s(%s)" with "cryptd(%s(%s))" in dm-crypt sources it locks up and doesn't work. > This would be inappropriate for upper layer code as they do not > know whether the underlying algorithm should be parallelised, > e.g., a PCI offload board certainly should not be parallelised. The upper layer should ideally request "cbc(aes)" and the crypto routine should select the most efficient implementation --- sync on single-core system, async with cryptd on multi-core system and async with hardware implementation if you have HIFN crypto card. > > 2) why not optimize software async crypto daemon (crypt/cryptd.c) instead > > of dm-crypt, so that all kernel subsystems can actually take advantage of > > those multi-CPU optimizations, not just dm-crypt? > > Because you cannot do what Andi is doing here in the crypto layer. > What dm-crypt does today (which hasn't always been the case BTW) > hides information away (the original submitting CPU) that we cannot > recreate. It is pointless to track the submitting CPU. Majority of time is consumed by raw encyption/decryption. And you must optimize that --- i.e. on SMP system make sure that cryptd distributes the work across all available cores. When you get this right --- i.e. when reading encrypted disk, you get either read speed equivalent to non-encrypted disk or all the cores are saturated, then you can start thinking about other optimizations. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
