false-sharing Questions
1
I am trying to understand a simple example and wonder why I don't see more false sharing than reported by perf c2c.
In my example (a matrix multiplication), two instances could cause false sharing ...
Drily asked 8/9 at 16:1
0
I have been experimenting with a simple true/false sharing benchmark, which does regular load+increment+write on a pointer. Basically this:
static void do_increments(volatile size_t *buffer, size_t...
Touraco asked 30/6 at 10:55
2
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Today I got a different understand with my professor on the Parallel Programming class, about what is "false sharing". What my professor said makes little sense so I pointed it out immediately. She...
Contraction asked 31/3, 2014 at 15:49
4
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While reading this question I encountered the terms “false sharing” and “true sharing”. I read what false sharing is, but I can’t find anything on true sharing. Although in the mentioned question t...
Plexus asked 22/8, 2019 at 9:40
1
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I found a comment from crossbeam.
Starting from Intel's Sandy Bridge, spatial prefetcher is now pulling pairs of 64-byte cache lines at a time, so we have to align to 128 bytes rather than 64.
Sou...
Circumcise asked 5/5, 2022 at 11:44
0
env : x86-64; linux-centos; 8-cpu-core
For testing 'false sharing performance' I wrote c++ code like this:
volatile int32_t a;
volatile int32_t b;
int64_t p1[7];
volatile int64_t c;
int64_t p...
Sanity asked 8/11, 2021 at 7:17
1
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Good day, I recently found an annotation introduced in Java 8 called Contended. From this mailing list I read what is false sharing and how annotation allows objects or fields to allocate an entire...
Prostitute asked 6/11, 2020 at 23:45
2
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Following static_assert passes in both gcc and clang trunk.
#include<mutex>
int main(){
static_assert(sizeof(std::mutex)==40);
}
Since x86 CPUs have 64 byte cache line I was expecting mutex...
Secern asked 2/10, 2020 at 11:7
1
I'm not used to post any question on the internet so please tell me if I'm doing something wrong.
In short
How to correctly prevent false sharing on a 64bits architecture with a CPU cacheline size...
Extreme asked 2/9, 2020 at 13:31
0
I know the answer could be that they did not prioritize it, but it really feels like intentional omission, they already have plenty of C++20 core language/library features and this C++17 feature is...
Lemmy asked 26/5, 2020 at 15:21
2
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For my bachelor thesis I have to analyse the effecs of False Sharing on multicore systems. So looking for the different cache-coherence-protocol-types I have come across on Wikipedia that Intel has...
Suddenly asked 7/8, 2015 at 11:37
1
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Consider the following example that proves false sharing existence:
using type = std::atomic<std::int64_t>;
struct alignas(128) shared_t
{
type a;
type b;
} sh;
struct not_shared_t
{
al...
Klotz asked 8/5, 2020 at 4:27
2
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Assuming that there are three pieces of data that I need from a heavily contended cache line, is there a way to load all three things "atomically" so as to avoid more than one roundtrip to any othe...
Heartstricken asked 30/5, 2019 at 21:21
3
While doing some research about lock-free/wait-free algorithms, I stumbled upon the false sharing problem. Digging a bit more led me to Folly's source code (Facebook's C++ library) and more specifi...
Socialism asked 22/3, 2015 at 20:59
2
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Look at this snippet:
#include <atomic>
#include <thread>
typedef volatile unsigned char Type;
// typedef std::atomic_uchar Type;
void fn(Type *p) {
for (int i=0; i<500000000; i+...
Ladybird asked 24/10, 2017 at 19:57
2
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If I have a C++ program with OpenMP parallelization, where different threads constantly use some small shared array only for reading data from it, does false sharing occur in this case? in other wo...
Chinua asked 6/7, 2017 at 9:23
2
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I have the following task to demonstrate false sharing and wrote a simple program:
#include <sys/times.h>
#include <time.h>
#include <stdio.h>
#include <pthread.h>
long ...
Slowmoving asked 30/11, 2011 at 18:51
1
Consider:
class Vector
{
double x, y, z;
// …
};
class Object
{
Vector Vec1, Vec2;
std::mutex Mtx1, Mtx2;
void ModifyVec1() { std::lock_guard Lock(Mtx1); /* … */ }
void ModifyVec2() { std:...
Formless asked 16/9, 2016 at 11:6
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For my bachelor thesis I have to evaluate common problems on multicore systems.
In some books I have read about false sharing and in other books about cache-line-ping-pong. The specific problems s...
Inconstant asked 6/6, 2015 at 16:18
1
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Recently, I had answered a question about optimizing a likely parallelizable method for generation every permutation of arbitrary base numbers. I posted an answer similar to the Parallelized, poor ...
Afteryears asked 23/4, 2015 at 5:3
3
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Are there any tools that detect and report False Sharing for applications written in C or C++?
Ferbam asked 16/8, 2011 at 14:36
1
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If we have two cores which read and write to different memory position in the same cache block, both cores are forced to reload that cache block again and again, although it is logically not necess...
Mortal asked 28/1, 2015 at 18:10
2
I have started learning how to use OpenMP as part of a University course. As a lab excercise, we have been given a serial program which we need to parallelize.
One of the first things we were mad...
Guevara asked 9/10, 2013 at 17:9
1
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Edit: ST does not allow to post more than two links for newbies. Sorry for the missing references.
I'm trying to reduce locking overhead in a C application where detecting changes on a global stat...
Abstemious asked 25/9, 2012 at 23:4
2
Solved
Can any one please share me the knowledge of "False Sharing" in Parallel programming .net 4.0 ? Would be great if you can explain with an example. Thanks in advance . i want the maximum performance...
Ultramicroscopic asked 11/8, 2011 at 13:51
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