> You know, you're talking to somebody who writes graphics drivers for a living :)
That's great. Why do you think you are the only one?
And what should I believe exactly here? That there is a syscall in every OpenGL API? If you are writing drivers you know it's not true yourself. The syscall overhead is not laughable, it's tens of thousands of clocks.
>Also, the vast majority of driver CPU time is spent in user space building up command submissions.
Exactly. OpenGL system (if you want to call it "driver" be my guest, DirectX does not do that for example, neither do other APIs) works mostly in the user space.
> The final command submission itself isn't free of course, but clearly more time is spent processing precisely those glDraw*() calls that you seem to think don't matter.
??? I don't even know what are you arguing here. Let's rewind.
Someone said that "driver calls" are expensive. And it's true for people who understand drivers as a part of OS, not "user mode drivers", which are just shared libs. I corrected, saying that there is no actual driver call in the sense that people understand, i.e. there is no OS call or "syscall" since the OpenGL "driver" is mostly a shared library in the user space. You seem to agree with me.
Now, I am well aware that some calls are expensive. I even know why. Some are not though. On some the overhead of moving data from a managed language to the GPU will be much greater than the call itself. E.g. setting an index buffer.
It still does not make it true that there are syscalls in the OpenGl calls anyways.
That's great. Why do you think you are the only one? And what should I believe exactly here? That there is a syscall in every OpenGL API? If you are writing drivers you know it's not true yourself. The syscall overhead is not laughable, it's tens of thousands of clocks.
>Also, the vast majority of driver CPU time is spent in user space building up command submissions.
Exactly. OpenGL system (if you want to call it "driver" be my guest, DirectX does not do that for example, neither do other APIs) works mostly in the user space.
> The final command submission itself isn't free of course, but clearly more time is spent processing precisely those glDraw*() calls that you seem to think don't matter.
??? I don't even know what are you arguing here. Let's rewind. Someone said that "driver calls" are expensive. And it's true for people who understand drivers as a part of OS, not "user mode drivers", which are just shared libs. I corrected, saying that there is no actual driver call in the sense that people understand, i.e. there is no OS call or "syscall" since the OpenGL "driver" is mostly a shared library in the user space. You seem to agree with me. Now, I am well aware that some calls are expensive. I even know why. Some are not though. On some the overhead of moving data from a managed language to the GPU will be much greater than the call itself. E.g. setting an index buffer.
It still does not make it true that there are syscalls in the OpenGl calls anyways.