Dear Jonathan, Thank you very much for the information . I will switch to kfifo. The problem was that a lot of drivers, which are already in the kernel, seem to use sw_ring, I was following other driver's route to do it. There is no problem with the sw_ring if we follow the way it should be used. However, the motion integration algorithm requires that the data comes in immediately when it is available and don't lose data. This half full requirement poses some problems. If we set the buffer length too small, we could lose data if the CPU is accidently delayed. If we set the length too big, it will take a while for the data to come and the data becomes too old when it comes to user application. It would be better that we have a ring buffer that is long enough yet the poll will pass when there is only one sample in the ring buffer. Hopefully, this kfifo can do the job. Now that I understand the mechanism underneath, I will switch to kfifo for our driver resubmitted patch. Best regards, Ge GAO -----Original Message----- From: Jonathan Cameron [mailto:jic23@xxxxxxxxx] Sent: Wednesday, May 16, 2012 12:16 AM To: Ge Gao; Jonathan Cameron Cc: linux-iio@xxxxxxxxxxxxxxx Subject: Re: sw_ring.c poll problem On 5/16/2012 6:46 AM, Jonathan Cameron wrote: > > > Ge Gao<ggao@xxxxxxxxxxxxxx> wrote: > >> Dear all, >> I found that ring_sw.c the poll function has to read half of the >> data for poll to work. Basically, you have to fill half of the ring >> buffer in order for poll to be triggrerred. You have to also read >> more than half of the data for poll to be disappeared. This would >> pose problems. If you have big ring buffer, the data will lost its >> immediacy. If you have small ring buffer, the data could lost if not >> buffered enough. Is that possible this poll action configurable? Or I >> missed anything. > > Use kfifobuf instead. Sw _ring is going away anyway. Hi Ge, I realised after sending that message that I was being rather dismissive of your query. Got up far too early this morning (as every morning ;) Anyhow, to give more details. sw_ring is probably never going to make it out of staging, hence the move to kfifo_buf. At somepoint we need to work out how to do equivalent functionality of sw_ring but I've not had time to more than start looking into this. As you saw, poll on sw_ring is a watershead signal indicating (in theory and last I checked it worked) that the ring is more than half full. Any read that takes the fill level below half (test code just reads half the size of the buffer), should allow a new passing of the watershead to resignal poll. It's entirely possible there is a bug in there though I know it is been getting a fair bit of testing with some other drivers so could be todo with the precise way you are reading it hitting some corner case? (I'm stretching...) Right now I'd just move over to kfifo_buf if I were you. It's much more 'standard' in that it's a fifo and poll indicates if there is anything there at all. >> Thanks. >> >> Best regards, >> >> Ge GAO >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-iio" >> in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo >> info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
