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Re: Data layout + false sharing
On Wednesday 02 December 2009 23:26:49 Mindaugas Rasiukevicius wrote:
> Group related structures and/or their members so they will be in the same
> cache line and during synchronisation wont touch other ones? How exactly,
> that is specific to your application.
Here is an example:
uint32_t threads_alloc; /* number of threads allocated to this group */
uint64_t threads_status; /* bitmask of which threads are
busy/free. 1=busy */
pthread_mutex_t mutex;/* protects threads_status */
ptf_thread_t *thread_list;/* array of threads */
The above structure represents a group of threads. It is accessed every time
application needs to schedule free threads to execute a task.
threads_alloc and thread_list variables are initialised once and stay
constant, threads_status is updated every time a thread is assigned a task, or
when a thread finishes a task and becomes free.
I think what I need to do is to add some padding around threads_status
variable, so that updating it does not invalidate cache line that holds values
for the variables that sit next to it.
What's the usual practice for doing that?
uint8_t pad0[cache_line / 8 ];
uint8_t pad1[cache_line / 8];
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