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Date: Wed, 28 Oct 2015 15:45:40 +0530 From: Muni Sekhar <munisekharrms@...il.com> To: Clemens Ladisch <clemens@...isch.de> Cc: linux-kernel@...r.kernel.org Subject: Re: character driver - poll() timeout On Wed, Oct 28, 2015 at 12:54 PM, Clemens Ladisch <clemens@...isch.de> wrote: > Muni Sekhar wrote: >> On Tue, Oct 27, 2015 at 8:48 PM, Clemens Ladisch <clemens@...isch.de> wrote: >>> Muni Sekhar wrote: >>>> I need to find out when exactly driver's poll callback returned timeout. >>> >>> Your poll callback _cannot_ return a timeout. >>> >>> Why do you think you need this information for? >> >> During stress test, my test application fails and throws poll() timeout error. >> >> I need to debug what is the state of my driver during that time. I >> added prints in driver poll(), but I gets lots of debug prints if >> poll() timeout is more. > > Your poll() callback does not really change the state of the driver. > It just returns the wait queue and the current state of the device. > (Which means it is likely to get called _twice_, before poll() goes > to sleep, and just before it returns.) > > Your driver's state changes only when > 1) you start some operation (such as read() or write()), or when > 2) you finish some operation (which wakes up anyone waiting on > that wait queue). > > If you time out, it means that some wake_up() happens too late or > not at all, or that you do not return the correct state. Thanks Clemens for the clarification. > > > Regards, > Clemens -- Thanks, Sekhar -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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