On Mon, 16 Sep 2019 17:20:28 -0500 Rob Herring robh@kernel.org wrote:
On Fri, Sep 13, 2019 at 6:17 AM Boris Brezillon boris.brezillon@collabora.com wrote:
The READ/WRITE flags are particularly useful if we want to avoid serialization of jobs that read from the same BO but never write to it.
Any data on performance differences?
Unfortunately no. When I initially added support for BO flags I thought it would fix a regression I had on one glmark2 test (ideas), but the problem ended up being something completely different (overhead of calling ioctl(WAIT_BO) on already idle BOs).
I just ran glmark2 again, and there doesn't seem to be a noticeable improvement with those 2 patches applied (and mesa patched to use the new flags). This being said, the improvement is likely to be workload dependent, so I wouldn't consider these patches as useless, but I'm fine putting them on hold until we see a real need.
Maybe Steven has some real use cases that could help outline the benefit of these patches.
The NO_IMPLICIT_FENCE might be useful when the user knows the BO is shared but jobs are using different portions of the buffer.
Why don't we add this when it is useful rather than might be?
I don't have a need for that one yet, but etanviv has it in place so I thought I'd add both at the same time. Note that it could help us reduce the number of fence returned by panfrost_job_dependency(), but I'm not sure it makes a difference in terms of perfs.