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. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- 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/
