On Sun, 2010-09-19 at 08:43 -0300, Mauro Carvalho Chehab wrote: > Hi Hans, >
> A per-dev lock may not be good on devices where you have lots of interfaces, > and that allows > more than one stream per interface. > > So, I did a different implementation, implementing the mutex pointer per file > handler. > On devices that a simple lock is possible, all you need to do is to use the > same locking > for all file handles, but if drivers want a finer control, they can use a > per-file handler > lock. > > I'm adding the patches I did at media-tree.git. I've created a separate > branch there (devel/bkl): > http://git.linuxtv.org/media_tree.git?a=shortlog;h=refs/heads/devel/bkl > > I've already applied there the other BKL-lock removal patches I've sent > before, plus one new > one, fixing a lock unbalance at bttv poll function (changeset 32d1c90c85). > > The v4l2 core patches are at: > > http://git.linuxtv.org/media_tree.git?a=commit;h=285267378581fbf852f24f3f99d2e937cd200fd5 > http://git.linuxtv.org/media_tree.git?a=commit;h=5f7b2159c87b08d4f0961c233a2d1d1b87c8b38d > > The approach I took serializes open, close, ioctl, mmap, read and poll, e. g. > all file operations > done by the V4L devices. Hi Mauro, I took a look at your changes in the first link. The approach seems like it serializes too much for one fd, and not enough for multiple fd's opened on the same device node. for a single fd, ioctl() probably doesn't need to be serialized against read() and poll() at all - at least for drivers that only provide the read I/O method. read() and poll() on the same device node in most cases can access to shared data structure in kernel using test_bit() and atomic_read(). poll() usually just needs to check if a count is > 0 in some incoming buffer count or incoming byte count somewhere, right? Multiple opens of the device node (e.g one fd for streaming, one fd for control) is what MythTV does, so the locking on a per fd basis doesn't work there. Regards, Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
