Re: [Valgrind-developers] [LLVMdev] [GSoC 2014] Using LLVM as a code-generation backend for Valgrind

[Patrick J. L. <lop...@gm...>]

On Wed, Feb 26, 2014 at 7:16 AM, Julian Seward <js...@ac...> wrote:
>
>
> What would make Valgrind faster is
>
> (1) improve the caching of guest registers in host registers across
>     basic block boundaries.  Currently all guest registers cached in
>     host registers are flushed back into memory at block boundaries,
>     and no host register holds any live value across the boundary.
>     This is simple but very suboptimal, creating large amounts of
>     memory traffic.

Sounds more like large amounts of L1 cache traffic.

> I suspect that the combination of (1) and (2) causes processor write
> buffers to fill up and start stalling, although I don't have numbers
> to prove that.

Maybe, but maybe not.  (3) and (especially) (4) might well have greater impact.

It is notoriously difficult to guess where a modern CPU is spending
its time without a profiler. Random memory access is of course a
disaster, but that sounds more like (4) than (1) or (2).

It would be very interesting to see a micro-profile of Valgrind.

 - Pat