[OE-core] [PATCH 1/1] db: disable the ARM assembler mutex code

[Andre McCurdy]

On Thu, Jun 14, 2018 at 12:24 PM, Khem Raj <raj.khem at gmail.com> wrote:
> On Thu, Jun 14, 2018 at 12:12 PM Andre McCurdy <armccurdy at gmail.com> wrote:
>>
>> On Thu, Jun 14, 2018 at 9:40 AM, Khem Raj <raj.khem at gmail.com> wrote:
>> > On 6/14/18 5:10 AM, Herve Jourdain wrote:
>> >> Hi,
>> >>
>> >> I believe I solved that same problem by just adding, in the case of armv8
>> >> (which I believe may be the new architecture you're referring to):
>> >> MUTEX_armv8 = ""
>> >> This way, it allows previous versions to work just like they did before,
>> >> without having to disable ARM assembler mutex code for architectures that
>> >> support it correctly - up to armv7ve I believe.
>> >> Of course, we might need to also have a good definition for armv8, which is
>> >> the object of another thread.
>> >
>> > right thats a better approach.
>>
>> SWP is not guaranteed to work on SMP systems... and even if it does,
>> performance is likely to be worse than the pthreads version (which can
>> take advantage of the newer instructions).
>>
>>   https://community.arm.com/processors/b/blog/posts/locks-swps-and-two-smoking-barriers
>>
>> In general, use of hand optimised assembler mutex implementations in
>> user space isn't something to be encouraged - use pthreads (or maybe a
>> gcc intrinsic) instead.
>>
>
> question is about disabling it on old arm machines, do we have data where
> we know that other sync methods without swp works better on armv5 and lower ?

On armv5 and below a hand optimised implementation using SWP is likely
to be faster than pthreads. No one is suggesting otherwise.

On SMP (highly likely nowadays for armv7 and above), SWP simply might
not work (aside from the fact that if it does work, it's likely to be
slower than pthreads). It's not really a question of performance
there, so the proposal to only disable SWP for armv8 doesn't seem like
a safe solution.

Using pthreads unconditionally is safe and easy. Unless you can prove
that hand optimised SWP is really a big win for armv5 (is anyone
really running a performance critical database on an armv5 system?)
why not keep the recipe simple and use pthreads everywhere?

>> I think the original patch is good.
>>
>> >> Cheers,
>> >> Herve
>> >>
>> >> -----Original Message-----
>> >> From: openembedded-core-bounces at lists.openembedded.org
>> >> [mailto:openembedded-core-bounces at lists.openembedded.org] On Behalf Of
>> >> Ovidiu Panait
>> >> Sent: jeudi 14 juin 2018 13:55
>> >> To: openembedded-core at lists.openembedded.org
>> >> Subject: [OE-core] [PATCH 1/1] db: disable the ARM assembler mutex code
>> >>
>> >> The swpb in macro MUTEX_SET will cause "undefined instruction" error on the
>> >> new arm arches which don't support this assembly instruction any more. If
>> >> use ldrex/strex to replace swpb, the old arm arches don't support them. So
>> >> to avoid this issue, just disable the ARM assembler mutex code, and use the
>> >> default pthreads mutex.
>> >>
>> >> Signed-off-by: Li Zhou <li.zhou at windriver.com>
>> >> Signed-off-by: Catalin Enache <catalin.enache at windriver.com>
>> >> Signed-off-by: Ovidiu Panait <ovidiu.panait at windriver.com>
>> >> ---
>> >>  meta/recipes-support/db/db_5.3.28.bb | 13 +------------
>> >>  1 file changed, 1 insertion(+), 12 deletions(-)
>> >>
>> >> diff --git a/meta/recipes-support/db/db_5.3.28.bb
>> >> b/meta/recipes-support/db/db_5.3.28.bb
>> >> index 093ee44909..15b4155a29 100644
>> >> --- a/meta/recipes-support/db/db_5.3.28.bb
>> >> +++ b/meta/recipes-support/db/db_5.3.28.bb
>> >> @@ -59,18 +59,7 @@ FILES_SOLIBSDEV = "${libdir}/libdb.so
>> >> ${libdir}/libdb_cxx.so"
>> >>  # All the --disable-* options replace --enable-smallbuild, which breaks a
>> >> bunch of stuff (eg. postfix)  DB5_CONFIG ?= "--enable-o_direct
>> >> --disable-cryptography --disable-queue --disable-replication
>> >> --disable-verify --disable-compat185 --disable-sql"
>> >>
>> >> -EXTRA_OECONF = "${DB5_CONFIG} --enable-shared --enable-cxx --with-sysroot"
>> >> -
>> >> -# Override the MUTEX setting here, the POSIX library is -# the default -
>> >> "POSIX/pthreads/library".
>> >> -# Don't ignore the nice SWP instruction on the ARM:
>> >> -# These enable the ARM assembler mutex code, this won't -# work with thumb
>> >> compilation...
>> >> -ARM_MUTEX = "--with-mutex=ARM/gcc-assembly"
>> >> -MUTEX = ""
>> >> -MUTEX_arm = "${ARM_MUTEX}"
>> >> -MUTEX_armeb = "${ARM_MUTEX}"
>> >> -EXTRA_OECONF += "${MUTEX} STRIP=true"
>> >> +EXTRA_OECONF = "${DB5_CONFIG} --enable-shared --enable-cxx --with-sysroot
>> >> STRIP=true"
>> >>  EXTRA_OEMAKE += "LIBTOOL='./${HOST_SYS}-libtool'"
>> >>
>> >>  EXTRA_AUTORECONF += "--exclude=autoheader  -I ${S}/dist/aclocal
>> >> -I${S}/dist/aclocal_java"
>> >> --
>> >> 2.17.1
>> >>
>> >> --
>> >> _______________________________________________
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>> >> Openembedded-core at lists.openembedded.org
>> >> http://lists.openembedded.org/mailman/listinfo/openembedded-core
>> >>
>> >
>> >
>> >
>> > --
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