[mythtv-users] Fixed!: Nvidia Sync to Vblank pegging cpu in X

jim.herold at comcast.net jim.herold at comcast.net
Thu Dec 21 17:58:31 UTC 2006

>On Tue, 2006-12-19 at 20:11 -0600, Jim herold wrote:
>> Interestingly, it works, but increases the "wa" cpu usage in top,
>This is, BTW, a good thing.  "wa" is time spent by the CPU waiting for
>I/O.  IOW, the CPU has nothing it can do because _everything_ runnable
>is blocked on some I/O operation completing.  In this context it means
>that that one simple change changed one single process from operating in
>a mode of spinning the cpu on a NOOP to releasing the CPU for other
>tasks to take advantage of instead.  This is a most wonderful change!

>>  and therefore leaves less cpu idle time

>Don't mistake a CPU high in "wa" as a busy CPU.  "wa" is essentially
>idle CPU.  The only difference between truly idle and "wa" is that truly
>idle means there are no process that want to do anything.  "wa" means
>there are processes that want to do something but are blocked waiting
>for some data to be read/written to/from somewhere.  When a process is
>waiting in this mode, it gives up the CPU to let another process have it
>while the first process does it's waiting.

>> by roughly 20% when compared with just disabling the sync to vblank.

Thanks for the info, that's good to know.  I had assumed that wa was bad 'cause a process 
had CPU locked up unable to do anything.  Good to know that other processes can
jump in there if they have something to do.

Thanks again everybody for the help on this one!

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