On Wed, Oct 2, 2013 at 12:42 PM, Stephen Boyd <sb...@codeaurora.org> wrote: > On 10/02/13 10:27, Santosh Shilimkar wrote: >> On Wednesday 02 October 2013 01:22 PM, Stephen Boyd wrote: >>> On 10/02/13 10:14, Santosh Shilimkar wrote: >>>> On Wednesday 02 October 2013 01:09 PM, Will Deacon wrote: >>>>> On Wed, Oct 02, 2013 at 05:55:28PM +0100, Santosh Shilimkar wrote: >>>>>> The sched_clock code uses 2 levels of function pointers, >>>>>> sched_clock_func() >>>>>> and read_sched_clock() but the no sched_clock check in postinit() just >>>>>> checks read_sched_clock(). >>>>>> >>>>>> This leads to kernel falling back to jiffy based sched clock even in >>>>>> presence of sched_clock_func() which is not desirable. >>>>>> >>>>>> Fix the postinit() check to avoid the issue. Probably the issue is hidden >>>>>> so far on most of the arm SOCs because of already existing sched_clock >>>>>> registrations apart from arch_timer sched_clock. One can reproduce the >>>>>> issue by just have arch_timer as sched_clock >>>>> Isn't this just an issue with the arch timer driver not calling >>>>> setup_sched_clock? Instead, we munge around with sched_clock_func >>>>> directly, >>>>> which doesn't appear to be the way anybody else deals with this. >>>>> >>>> I thought about that option as well but was not sure since even in that >>>> case >>>> the check is not complete. We just ensure that function is popullated. >>> Yes, nothing is actually broken because sched_clock_func() won't try to >>> use the jiffy based read_sched_clock() function. I'm not sure we >>> actually need this patch besides to remove a useless timer that updates >>> the jiffy epoch. Can we wait until my 64-bit sched_clock patch series >>> lands in 3.13? It looks like I still need an ack from Will or Catalin on >>> the architected timer patch before the clocksource folks pick it up. >>> >> Really... I have not created patch out of fun. >> Its broken on my keystone machine at least where the sched_clock is >> falling back on jiffy based sched_clock even in presence of arch_timer >> sched_clock. > > How is that possible? sched_clock_func is only assigned by > arch/arm/kernel/arch_timer.c when the architected timer is detected and > sched_clock() in kernel/time/sched_clock.c calls that function pointer > unconditionally. The only way I see this happening is if the architected > timer rate is zero. I agree we will get two lines in the dmesg about > sched_clock and its not very clear which one is being used.
It does setup a timer to run to handle wrapping which should be harmless, but isn't needed. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
