property Origin: TLine Origin read f Origin write Set Origin default lo Top Left; property Pen: TPen read f Pen write Set Pen; property Height default 33; property Width default 33; procedure Style Changed(Sender: TObject); end; procedure Register; implementation procedure Register; begin Register Components('Samples', [TLine]); end; procedure TLine. Style Changed(Sender: TObject); begin Invalidate; end; constructor TLine.
It occurs when threads on different processors modify variables that reside on the same cache line, as illustrated in Figure 1.This article covers methods to detect and correct false sharing.This article is part of the larger series, "Intel Guide for Developing Multithreaded Applications," which provides guidelines for developing efficient multithreaded applications for Intel® platforms.For systems based on the Intel® Core™ 2 processor, configure VTune analyzer or Intel PTU to sample the events at the corresponding system at or near load/store instructions within threads to determine the likelihood that the memory locations reside on the same cache line and causing false sharing.Intel PTU comes with predefined profile configurations to collect events that will help to locate false sharing.Even though the threads modify different variables (red and blue arrows), the cache line is invalidated, forcing a memory update to maintain cache coherency.
To ensure data consistency across multiple caches, multiprocessor-capable Intel® processors follow the MESI (Modified/Exclusive/Shared/Invalid) protocol.
Avoiding and Identifying False Sharing Among Threads (PDF 218KB)Abstract In symmetric multiprocessor (SMP) systems, each processor has a local cache. False sharing occurs when threads on different processors modify variables that reside on the same cache line.
This invalidates the cache line and forces an update, which hurts performance.
In Figure 1, threads 0 and 1 require variables that are adjacent in memory and reside on the same cache line.
The cache line is loaded into the caches of CPU 0 and CPU 1 (gray arrows).
If the processor sees the same cache line which is now marked ‘M’ being accessed by another processor, the processor stores the cache line back to memory and marks its cache line as ‘Shared’.