mainlining shenanigans
f99973e18b
When the tick is stopped and we reach the dynticks evaluation code on IRQ exit, we perform a soft tick restart if we observe an expired timer from there. It means we program the nearest possible tick but we stay in dynticks mode (ts->tick_stopped = 1) because we may need to stop the tick again after that expired timer is handled. Now this solution works most of the time but if we suffer an IRQ storm and those interrupts trigger faster than the hardware clockevents min delay, our tick won't fire until that IRQ storm is finished. Here is the problem: on IRQ exit we reprog the timer to at least NOW() + min_clockevents_delay. Another IRQ fires before the tick so we reschedule again to NOW() + min_clockevents_delay, etc... The tick is eternally rescheduled min_clockevents_delay ahead. A solution is to simply remove this soft tick restart. After all the normal dynticks evaluation path can handle 0 delay just fine. And by doing that we benefit from the optimization branch which avoids clock reprogramming if the clockevents deadline hasn't changed since the last reprog. This fixes our issue because we don't do repetitive clock reprog that always add hardware min delay. As a side effect it should even optimize the 0 delay path in general. Reported-and-tested-by: Octavian Purdila <octavian.purdila@nxp.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1496328429-13317-1-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.