On Mon, 7 Nov 2005, David Lang wrote:
Brian,
If I am understanding the data you posted, it looks like you are useing
sched_yield extensivly in your database. This is known to have significant
problems on SMP machines, and even bigger ones on NUMA machines, in part
becouse the process doing the sched_yield may get rescheduled immediatly and
not allow other processes to run (to free up whatever resource it's waiting
for). This causes the processor to look busy to the scheduler and therefor
the scheduler doesn't migrate other processes to the CPU that's spinning on
sched_yield. On NUMA machines this is even more noticable as processes now
have to migrate through an additional layer of the scheduler.
I have an application designed on Linux where the only processes running are
'init' and those integral to the application. Each communicates using mutual
exclusion & semaphores across a shared file/memory backing.
The application was designed to be as close intrinsically as to what Linux
does--manage processes. There's only 1 thread per process, and each process has
a different executable for its own task.
One day I plan to extend this application across multiple CPUs using either SMP
or NUMA. Therefore a lot of the mutual exclusion routines I've coded in use
sched_yield().
What should I do instead to alleviate the problem of causing the processor to
look busy? In this case I _want_ other processes to be migrated over to the
CPU in order to free up the critical section faster.
A simple test using a 2-cpu SMP system resulted in sched_yield() being a lot
faster than using futexes, but I don't know for the NUMA case.
Best regards,
-Byron
--
Byron Stanoszek Ph: (330) 644-3059
Systems Programmer Fax: (330) 644-8110
Commercial Timesharing Inc. Email: [email protected]
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