Re: [boost] [thread] RFC standard proposed mutex, read-write mutex, condition

From: Howard Hinnant (howard.hinnant_at_[hidden])
Date: 2007-08-26 19:17:07

On Aug 26, 2007, at 4:49 PM, Peter Dimov wrote:

> Howard Hinnant:
>
>> I've been using "sizeof(condition)" as shorthand for "reducing L1
>> cache misses".  Your technique of moving the checking to a static map
>> (or unordered_map)<void*, void*> does indeed reduce the
>> sizeof(condition), but does not reduce L1 cache misses.
>
> map<> is the "debug" variation, there's also a "checked release"  
> one. They
> do reduce the L1 cache misses on the only path where these misses  
> can be
> measured, the path that does not call wait. Once you call wait, you  
> enter a
> blocking kernel call and L1 misses cease to be of importance.

My knowledge is not what it should be in this area.

If there are two threads sharing a processor, and one thread is  
accessing M1 amount of memory and the other thread is accessing M2  
amount of memory, and M1 + M2 is less than the L1 cache size, isn't  
that faster than if both M1 and M2 are less than the L1 cache size but  
M1 + M2 is larger than the L1 cache size?  I.e. can larger memory use  
(or more scattered memory use) on one thread make cache misses more  
likely on another thread?

-Howard