svn commit: r336025 - in head/sys: amd64/include i386/include
Rodney W. Grimes
freebsd at pdx.rh.CN85.dnsmgr.net
Fri Jul 6 15:52:04 UTC 2018
> On Fri, Jul 6, 2018 at 9:32 AM, Rodney W. Grimes <
> freebsd at pdx.rh.cn85.dnsmgr.net> wrote:
>
> > > Author: hselasky
> > > Date: Fri Jul 6 10:13:42 2018
> > > New Revision: 336025
> > > URL: https://svnweb.freebsd.org/changeset/base/336025
> > >
> > > Log:
> > > Make sure kernel modules built by default are portable between UP and
> > > SMP systems by extending defined(SMP) to include defined(KLD_MODULE).
> > >
> > > This is a regression issue after r335873 .
> > >
> > > Discussed with: mmacy@
> > > Sponsored by: Mellanox Technologies
> >
> > Though this fixes the issue, it also means that now when
> > anyone intentionally builds a UP kernel with modules
> > they are getting SMP support in the modules and I am
> > not sure they would want that. I know I don't.
> >
>
>
> On UP systems, these additional opcodes are harmless. They take a few extra
> cycles (since they lock an uncontested bus) and add a couple extra memory
> barriers (which will be NOPs). On MP systems, atomics now work by default.
> Had we not defaulted like this, all modules built outside of a kernel build
> env would have broken atomics. Given that (a) the overwhelming majority
> (99% or more) is SMP and (b) the MP code merely adds a few cycles to what's
> already a not-too-expensive operation, this was the right choice.
>
> It simply doesn't matter for systems that are relevant to the project
> today. While one could try to optimize this a little (for example, by
> having SMP defined to be 0 or 1, say, and changing all the ifdef SMP to if
> (defined(SMP) && SMP != 0)), it's likely not going to matter enough for
> anybody to make the effort. UP on x86 is simply not relevant enough to
> optimize for it. Even in VMs, people run SMP kernels typically even when
> they just allocate one CPU to the VM.
>
> So while we still support the UP config, and we'll let people build
> optimized kernels for x86, we've flipped the switch from pessimized for SMP
> modules to pessimized for UP modules, which seems like quite the reasonable
> trade-off.
>
> Were it practical to do so, I'd suggest de-orbiting UP on x86. However,
> it's a lot of work for not much benefit and we'd need to invent much crazy
> to get there.
Trivial to fix this with
+#if defined(SMP) || !defined(_KERNEL) || defined(KLD_MODULE) || !defined(KLD_UP_MODULES)
>
> Warner
>
>
> > > Modified:
> > > head/sys/amd64/include/atomic.h
> > > head/sys/i386/include/atomic.h
> > >
> > > Modified: head/sys/amd64/include/atomic.h
> > > ============================================================
> > ==================
> > > --- head/sys/amd64/include/atomic.h Fri Jul 6 10:10:00 2018
> > (r336024)
> > > +++ head/sys/amd64/include/atomic.h Fri Jul 6 10:13:42 2018
> > (r336025)
> > > @@ -132,7 +132,7 @@ void atomic_store_rel_##TYPE(volatile
> > u_##TYPE *p, u_
> > > * For userland, always use lock prefixes so that the binaries will run
> > > * on both SMP and !SMP systems.
> > > */
> > > -#if defined(SMP) || !defined(_KERNEL)
> > > +#if defined(SMP) || !defined(_KERNEL) || defined(KLD_MODULE)
> > > #define MPLOCKED "lock ; "
> > > #else
> > > #define MPLOCKED
> > > @@ -354,7 +354,7 @@ atomic_testandclear_long(volatile u_long *p, u_int
> > v)
> > > */
> > > #define OFFSETOF_MONITORBUF 0x100
> > >
> > > -#if defined(SMP)
> > > +#if defined(SMP) || defined(KLD_MODULE)
> > > static __inline void
> > > __storeload_barrier(void)
> > > {
> > >
> > > Modified: head/sys/i386/include/atomic.h
> > > ============================================================
> > ==================
> > > --- head/sys/i386/include/atomic.h Fri Jul 6 10:10:00 2018
> > (r336024)
> > > +++ head/sys/i386/include/atomic.h Fri Jul 6 10:13:42 2018
> > (r336025)
> > > @@ -143,7 +143,7 @@ void atomic_subtract_64(volatile
> > uint64_t *, uint64_t
> > > * For userland, always use lock prefixes so that the binaries will run
> > > * on both SMP and !SMP systems.
> > > */
> > > -#if defined(SMP) || !defined(_KERNEL)
> > > +#if defined(SMP) || !defined(_KERNEL) || defined(KLD_MODULE)
> > > #define MPLOCKED "lock ; "
> > > #else
> > > #define MPLOCKED
> > > @@ -302,7 +302,7 @@ atomic_testandclear_int(volatile u_int *p, u_int v)
> > > */
> > >
> > > #if defined(_KERNEL)
> > > -#if defined(SMP)
> > > +#if defined(SMP) || defined(KLD_MODULE)
> > > #define __storeload_barrier() __mbk()
> > > #else /* _KERNEL && UP */
> > > #define __storeload_barrier() __compiler_membar()
> > >
> > >
> >
> > --
> > Rod Grimes
> > rgrimes at freebsd.org
> >
> >
--
Rod Grimes rgrimes at freebsd.org
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