> -----Original Message----- > From: linux-fbdev-owner at vger.kernel.org [mailto:linux-fbdev- > owner at vger.kernel.org] On Behalf Of Maarten Lankhorst > Sent: Monday, May 13, 2013 8:41 PM > To: Inki Dae > Cc: 'Rob Clark'; 'Daniel Vetter'; 'DRI mailing list'; linux-arm- > kernel at lists.infradead.org; linux-media at vger.kernel.org; 'linux-fbdev'; > 'Kyungmin Park'; 'myungjoo.ham'; 'YoungJun Cho' > Subject: Re: Introduce a new helper framework for buffer synchronization > > Op 13-05-13 13:24, Inki Dae schreef: > >> and can be solved with userspace locking primitives. No need for the > >> kernel to get involved. > >> > > Yes, that is how we have synchronized buffer between CPU and DMA device > > until now without buffer synchronization mechanism. I thought that it's > best > > to make user not considering anything: user can access a buffer > regardless > > of any DMA device controlling and the buffer synchronization is > performed in > > kernel level. Moreover, I think we could optimize graphics and > multimedia > > hardware performance because hardware can do more works: one thread > accesses > > a shared buffer and the other controls DMA device with the shared buffer > in > > parallel. Thus, we could avoid sequential processing and that is my > > intention. Aren't you think about that we could improve hardware > utilization > > with such way or other? of course, there could be better way. > > > If you don't want to block the hardware the only option is to allocate a > temp bo and blit to/from it using the hardware. > OpenGL already does that when you want to read back, because otherwise the > entire pipeline can get stalled. > The overhead of command submission for that shouldn't be high, if it is > you should really try to optimize that first > before coming up with this crazy scheme. >
I have considered all devices sharing buffer with CPU; multimedia, display controller and graphics devices (including GPU). And we could provide easy-to-use user interfaces for buffer synchronization. Of course, the proposed user interfaces may be so ugly yet but at least, I think we need something else for it. > In that case you still wouldn't give userspace control over the fences. I > don't see any way that can end well. > What if userspace never signals? What if userspace gets killed by oom > killer. Who keeps track of that? > In all cases, all kernel resources to user fence will be released by kernel once the fence is timed out: never signaling and process killing by oom killer makes the fence timed out. And if we use mmap mechanism you mentioned before, I think user resource could also be freed properly. Thanks, Inki Dae > ~Maarten > -- > To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in > the body of a message to majordomo at vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
