Re: [Ocf-linux-users] talitos driver should be preemtive

[Kim P. <kim...@fr...>]

On Mon, 24 May 2010 23:14:55 +0200
" ALEXANDRU IONUT GRAMA" <ai....@al...> wrote:

> Hello. My name is Alexandru and I'm doing my final degree project about
> porting Linux to a embedded device (a router), that uses a 8272 of
> Freescale. My issue to solve is provide IPsec to the router. The
> software that I used is a Linux 2.6.19 + Quagga + Openssl + ipsec-tools.
> The point was that the processor (8272) came with a crypto-processor
> embedded in it that should help in the encryption process. I've found
> this excelent project that provide the support of hardware encryption
> with Cryptodev + Talitos driver. Also, the patch for Openssl works
> perfectly and I've obtained the feature that I need.
> 
> After making some benchmarks I've discovered that talitos is not
> preemtive. The crypto-processor (SEC) should make the operations of
> encryption/decryption and let the processor idle; the scheduler should
> be called and let another process to enter as "active process". After
> the crypto-processor finish the job, it should say "I'm done!" by a
> IRQ signal and the other encryption process that need the encrypted data
> should be activated and continue getting the crypted data from the
> address of memory where the crypto-processor writted it.
> 
> Well, the behaviour of talitos seems not to be like that. It's look like
> the processor is waiting for the crypto-processor to finish, and after
> that it gets the crypted data.That wastes the time of the processor
> while is waiting for the crypto-processor to finish. Maybe I'm wrong,
> but the benchmarks looks like (2 processes means 1 crypting and another
> doing an infinite loop a=1+1):
>                    no CD(R) no CD(U)  no CD (S)
> 1 process crypting 0.36     0.13        0.20
> 2 processes(1+1*)    0.72     0.13        0.20
> It looks normal without Cryptodev that the user and system time be the
> same, but the the real be double, because there's another process
> requiring the CPU.
> 
> Benchmarking the system with Cryptodev I've obtain the more or less the
> same times (much more system time that without it), but it's not
> exactly the double, it's 0,02 less (0.36*2 - 0.02). That's it
> improving the time, but not really how much I've expected. And it is
> because crypto-processor doesn't leave free the processor.
> 
> I want to add preemtion to talitos, does anyone is working already on it?
> May I help?

I believe this is due to the wait_event_interruptible call in cryptodev.

Also note that there are other pre-emption issues due to openssl having
a synchronous crypto api (at least last I checked) - that tends to not
jive well with asynchronous crypto h/w, such as what you are using.

Kim