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

Brian J. Murrell brian at interlinx.bc.ca
Wed Dec 20 23:43:58 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.


My other computer is your Microsoft Windows server.

Brian J. Murrell
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