Re: [PATCH 1/1] db: disable the ARM assembler mutex code

[Khem Raj <raj.khem@gmail.com>]

On Thu, Jun 14, 2018 at 12:12 PM Andre McCurdy <armccurdy@gmail.com> wrote:
>
> On Thu, Jun 14, 2018 at 9:40 AM, Khem Raj <raj.khem@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 ? Do
we have gcc intrinsics for those versions of arm ?
if we do then I think I would agree

> I think the original patch is good.
>
> >> Cheers,
> >> Herve
> >>
> >> -----Original Message-----
> >> From: openembedded-core-bounces@lists.openembedded.org
> >> [mailto:openembedded-core-bounces@lists.openembedded.org] On Behalf Of
> >> Ovidiu Panait
> >> Sent: jeudi 14 juin 2018 13:55
> >> To: openembedded-core@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@windriver.com>
> >> Signed-off-by: Catalin Enache <catalin.enache@windriver.com>
> >> Signed-off-by: Ovidiu Panait <ovidiu.panait@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
> >>
> >> --
> >> _______________________________________________
> >> Openembedded-core mailing list
> >> Openembedded-core@lists.openembedded.org
> >> http://lists.openembedded.org/mailman/listinfo/openembedded-core
> >>
> >
> >
> >
> > --
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