Enhanced rep movsb stosb. [PATCH 1/5] x86_64: use REP MOVSB in copy_page()

ERMS is extremely slow for small sizes. There are far more efficient ways to move data. The correct area is obtained by starting with original data in currentapplying all the triplets in the current set, using memcpy provided by the C library, and copying the current area to correct. Post as a guest Name. If you want the higher speeds you are seeing from from memcpy, you can dig up the source for it.

 

An instance of enhanced REP STOSB with ECX= is decoded as a long micro-op flow provided by hardware, but retires as one instruction. There.So it is both a software maintenance benefit no need to change source and a benefit for existing binaries no need to deploy new binaries to take advantage of the improvement.

 

rutex.online › Intel-C-Compiler › td-p.For example, the Intel manual has Figure

 

Solved: This question is about assembly code. Many people believe that the implementation of 'enhanced rep movsb/stosb' obtains an aligned address.It certainly still uses a non-RFO protocol, at least for large copies, since it gets performance that is really only possible with non-RFO this is most obvious for stosb but it applies to the mov variants too.

 

This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).Jim seems to have answered your question.

 

Enhancement availability is indicated by CPUIDEBX[9] (Enhanced REP MOVSB/STOSB). Intel 64 and IA SDM and performance optimization guide may include.Intel Optimization Manual 2.

 

The newer Intel processors support Enhanced REP MOVSB/STOSB (ERMS) which has a feature bit in CPUID. This patch adds the Enhanced REP MOVSB/STOSB (ERMS) bit.So on other platforms you might find that NT stores are less useful at least when you care about single-threaded performance and perhaps rep movsb wins where if it gets the best of both worlds.

 

REP STOS/MOVS is the right way to move memory now, and its operands are SI, now recommend 'implementing memcpy using Enhanced REP MOVSB and STOSB might.Is this related to this bit from the Intel Optimization Manual.

 

X86 memcpy: use REPMOVSB instead of REPMOVS{Q,D,W} for inline copies when the Enhanced REP MOVSB and STOSB operation (ERMSB).Here are my results on the same system from tinymembnech.

 

The newer Intel processors support Enhanced REP MOVSB/STOSB (ERMS) which has a feature bit in CPUID. This patch adds the Enhanced REP MOVSB/STOSB.Show 6 more comments.

 

On my Broadwell-era Xeon copying page with REP MOVSB is ~% faster than with REP MOVSQ. Some CPUs are adding enhanced REP MOVSB/STOSB instructions.This question is about assembly code.

 

Enhanced REP MOVSB/STOSB, Enables or disables Enhanced REP MOVSB/STOSB support. This setting can affect performance, depending on the application running on.It draw on the above and introduces a few new ideas.Forum Enhanced rep movsb stosb

 

Table 1.

 

Here you might be forced to use only older instruction sets, which rules out any AVX, etc.

 

If you study your library's implementation, you will probably be amazed.

 

View solution in original post.

 

For example, architectures may have wider internal data paths that the ISA exposes 5 and rep movs could use that internally.

 

GCC does exactly this see e.

 

The combination of fairly low memory latency and modest 2-channel bandwidth means this particular chip happens to be able to saturate its memory bandwidth from a single-thread, which changes the behavior dramatically.

 

That has to happen to make room in the ROB for following uops.

 

forum? I want to hear more about that.

 

It would be interesting to see tingybenchmark on a Ivy Bridge system.

 

Why I am going on and on about this?

 

As copy sizes get much larger, however, the relative importance of this diminishes rapidly e.

 

Here are my results on the same system from tinymembnech.

 

Asked 4 years, 11 months ago.

 

However, even here there are reports of the opposite result on earlier hardware like Ivy Bridge.

 

Yes, exactly.

 

Code Size The executed code size a few bytes is microscopic compared to a typical optimized memcpy routine.

 

LGTM too.

 

This turns turbo back on so I had to disable turbo after.

 

When a rep movs instruction is issued, the CPU knows that an entire block of a known size is to be transferred.