# event synchronization on multiple device context

**URL:** <https://forums.developer.nvidia.com/t/event-synchronization-on-multiple-device-context/16744>\
**Category:** CUDA Programming and Performance\
**Created:** [May 23, 2010, 7:50am UTC](https://forums.developer.nvidia.com/t/event-synchronization-on-multiple-device-context/16744 "2010-05-23T07:50:26Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![tzachi](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@tzachi](https://forums.developer.nvidia.com/u/tzachi)\
**Post date:** [May 23, 2010, 7:50am UTC](https://forums.developer.nvidia.com/t/event-synchronization-on-multiple-device-context/16744/1 "2010-05-23T07:50:26Z")

</div>

i am working on window 7 and driver 197.45.

i notice that when trying to synchronize two command queues that belong to different devices the synchronization is cpu blocking even if the flag ‘blocking\_write/read’ is explicitly set to ‘CL\_FALSE’.

i created a multiple device context and called : ‘clEnqueueWriteBuffer’ with ‘blocking\_write’ parameter set to CL\_FALSE. the command was also dependent on an event that is generated by a call to ‘clEnqueueReadBuffer’ with a command queue which is associated with a different gpu.

This is a major performance bottleneck which took me a week to figure out!!!  
I here by call to the openCL team to fix it at once !!

Tzachi