Re: [RFC 12/12] iscsi-target: Add Makefile/Kconfig and update TCM top level

On Thu, 2011-03-03 at 09:19 -0500, Christoph Hellwig wrote:

On Wed, Mar 02, 2011 at 01:32:11PM -0800, Nicholas A. Bellinger wrote:

quoted

The kernel code itself that is specific to using the SSE v4.2
instruction for CRC32C offload are using #ifdef CONFIG_X86 stubs in
iscsi_target_login.c:iscsi_login_setup_crypto(), and !CONFIG_X86 will
default to using the unoptimized 1x8 slicing soft CRC32C code.  This
particular piece of logic has been tested on powerpc and arm and is
funcitoning as expected from the kernel level using the arch independent
soft code.

I don't think you need that code at all.  The crypto code is structured
to prefer the optimized implementation if it is present.  Just stripping
the x86-specific code out and always requesting the plain crc32c
algorithm should give you the optimized one if it is present on your
system.

Please give it a try.

This is what I originally thought as well, but this ended up not being
the case when the logic was originally coded up.   I just tried again
with .38-rc7 on a 5500 series machine and simply stubbing out the
CONFIG_X86 part from iscsi_login_setup_crypto() and calling:

   crypto_alloc_hash("crc32c", 0, CRYPTO_ALG_ASYNC)

does not automatically load and use crc32c_intel.ko when only requesting
plain crc32c.

The reason for the extra crypto_alloc_hash("crc32c-intel", ...) call in
iscsi_login_setup_crypto() is to load crc32c_intel.ko on-demand for
cpu_has_xmm4_2 capable machines.

I should mention this is with the following .config:

CONFIG_CRYPTO_CRC32C=y
CONFIG_CRYPTO_CRC32C_INTEL=m

This would seem to indicate that CRC32C_INTEL needs to be compiled in
(or at least manually loaded) for libcypto to use the optimized
instructions when the plain crc32c is called, correct..?

--nab