On 02/10/2014 10:49 PM, Stephen Boyd wrote: > On 02/07, John Stultz wrote: >> On 02/07/2014 02:22 PM, Stephen Boyd wrote: >>> On 02/07, Stephen Boyd wrote: >>>> If two sched_clock sources are registered we may end up in a >>>> situation where a call to sched_clock() may be accessing the >>>> epoch cycle count for the old counter and the cycle count for the >>>> new counter. This can lead to confusing results where >>>> sched_clock() values jump and then are reset to 0 (due to the way >>>> the registration function forces the epoch_ns to be 0). Fix this >>>> by reorganizing the registration function to hold the seqlock for >>>> as short a time as possible while we update the clock_data >>>> structure for a new counter and stop resetting the epoch_ns count >>>> to 0. >>> Hmm.. This won't properly accumulate time. We need to put >>> whatever time has elapsed into epoch_ns when we register the new >>> counter for this to work. I don't have a board with this >>> configuration but I'll send a v2 that should fix this. Hopefully >>> Will can test it. >> Also maybe clarify in the commit message that this is a result of not >> having the necessary locking in place in the registration code (likely >> due to it not really being required in the single clock case), just so >> Ingo and others have some more context as to why this is needed now and >> wasn't hit before. >> > Hmph... I already sent v2 before you replied. Is the commit text > good enough? I do mention that this is about two sched_clock > sources being registered. I'll tweak the commit message a bit make this point more clear. thanks -john _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/linux-arm-kernel