[firedrake] Measure fieldsplit/AMG setup time separately

[Lawrence Mitchell]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 08/04/15 11:31, Eike Mueller wrote:
> Dear firedrakers,
> 
> how can I enforce the setup of the entire PETSc solver when the 
> object is created? I use the fieldsplit preconditioner with AMG
> for the pressure space.
> 
> What I currently do is
> 
> up_problem = LinearVariationalProblem(a_up, L_up, vmixed, bcs=bcs)
>  up_solver = LinearVariationalSolver(up_problem, 
> solver_parameters=sparams) ksp = up_solver.snes.getKSP()
> ksp.setUp() pc = ksp.getPC() pc.setUp()
> 
> But that does not seem to work, since I still see that the first 
> iteration of the subsequent solve call is much larger.
> 
> I also noticed that on ARCHER the setup time is ridiculously large 
> (200x larger than 1 iteration), and I don’t observe this on my 
> laptop. Has anyone seem similar behaviour on ARCHER?

How many processes are you running this on?  The setup will form the
PC (at some level) which may need the assembled operators.  This in
turn will force computation which may require compilation of code (and
loading from disk cache).  If the disk is under stress this can be
expensive.

Lawrence
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEbBAEBAgAGBQJVJRGhAAoJECOc1kQ8PEYv+YoH91GBTqx/d+2L1jsuC6hjqQKo
Tq9LWB6vO2cG5TP3PJNg3DqCH5iJLEKBIV1KyDyP8yRN+jMo/oxn687hvK//eqrA
Fq9N3xzR9gxh3umQ0Rd9b7uYhIk20b8vk7k6mZJcuWJmUulv5sTZjFgrPtbfPvdC
OChfmrK3ER0QdRYJRI+2HidLHAMoX9YzWN/RTk7/VVSQMoG4S2b0s4zNKT2Z16QR
PgIYSI2L0JLWtUyoD+u8cXDwOxWSylbw3wkg+qIs5zLyp5aUUcZjrEdSe22vctC9
EeGB+2ulTPI9o4P7wfuP8XEPZYWSlY8fcQm4rXBsmJKuE0RTbwYy7I0fStkfEQ==
=DObK
-----END PGP SIGNATURE-----