search for: multicopy

On Wed, Jan 02, 2019 at 03:57:58PM -0500, Michael S. Tsirkin wrote: > @@ -875,6 +893,8 @@ to the CPU containing it. See the section on "Multicopy atomicity" > for more information. > > > + > + > In summary: > > (*) Control dependencies can order prior loads against later stores. Was this hunk intentional?

...> + > In addition, control dependencies apply only to the then-clause and > else-clause of the if-statement in question. In particular, it does > not necessarily apply to code following the if-statement: > @@ -875,6 +893,8 @@ to the CPU containing it. See the section on "Multicopy atomicity" > for more information. > > > + > + > In summary: > > (*) Control dependencies can order prior loads against later stores. > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h > index 92ec486a4f9e..b4934e8c...

...> + > In addition, control dependencies apply only to the then-clause and > else-clause of the if-statement in question. In particular, it does > not necessarily apply to code following the if-statement: > @@ -875,6 +893,8 @@ to the CPU containing it. See the section on "Multicopy atomicity" > for more information. > > > + > + > In summary: > > (*) Control dependencies can order prior loads against later stores. > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h > index 92ec486a4f9e..b4934e8c...

So as explained in Documentation/memory-barriers.txt e.g. a load followed by a store require a full memory barrier, to avoid store being ordered before the load. Similarly load-load requires a read memory barrier. Thinking about it, we can actually create a data dependency by mixing the first loaded value into the pointer being accessed. This adds an API for this and uses it in virtio. Written

...and let the codegen define what low-level instructions to use in each case. So, a processor without VFP would unroll the loop, while one with could use the VFP instructions instead of unrolling. Collapsing memset-like loop: multistore i32 %value, [ 400 x i32 ]* %array Collapsing memcpy-like loop: multicopy [ 400 x i32 ]* %orig, [ 400 x i32 ]* %dest Like the MSVC, we could also detect pointer copy loops and revert to a memcpy call. If a loop is called more than a few times, might be better (if space optimisations are not on) to create a region in memory to copy from with memcpy. This is particularly...

On Nov 7, 2009, at 4:15 PM, Renato Golin wrote: > 2009/11/7 Chris Lattner <clattner at apple.com>: >> I enjoyed this presentation: >> http://www.linux-kongress.org/2009/slides/compiler_survey_felix_von_leitner.pdf > > Wow, very comprehensive! > > Is there anyone working on vectorization? This is something that > interests me, I might give it a try, just need

...(b, q); + WRITE_ONCE(b, 1); + In addition, control dependencies apply only to the then-clause and else-clause of the if-statement in question. In particular, it does not necessarily apply to code following the if-statement: @@ -875,6 +893,8 @@ to the CPU containing it. See the section on "Multicopy atomicity" for more information. + + In summary: (*) Control dependencies can order prior loads against later stores. diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h index 92ec486a4f9e..b4934e8c551b 100644 --- a/arch/alpha/include/asm/barrier.h +++ b...

...n addition, control dependencies apply only to the then-clause and > > else-clause of the if-statement in question. In particular, it does > > not necessarily apply to code following the if-statement: > > @@ -875,6 +893,8 @@ to the CPU containing it. See the section on "Multicopy atomicity" > > for more information. > > + > > + > > In summary: > > (*) Control dependencies can order prior loads against later stores. > > diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h > > index 92ec486a4f9...