Messages in this thread | | | Date | Wed, 9 Feb 2022 20:58:27 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v3 0/7] arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys |
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On Wed, Feb 09, 2022 at 03:35:28PM +0000, Mark Rutland wrote: > This series enables PREEMPT_DYNAMIC on arm64. To do so, it adds a new > mechanism allowing the preemption functions to be enabled/disabled using > static keys rather than static calls, with architectures selecting > whether they use static calls or static keys. > > With non-inline static calls, each function call results in a call to > the (out-of-line) trampoline which either tail-calls its associated > callee or performs an early return. > > The key idea is that where we're only enabling/disabling a single > callee, we can inline this trampoline into the start of the callee, > using a static key to decide whether to return early, and leaving the > remaining codegen to the compiler. The overhead should be similar to > (and likely lower than) using a static call trampoline. Since most > codegen is up to the compiler, we sidestep a number of implementation > pain-points (e.g. things like CFI should "just work" as well as they do > for any other functions). > > The bulk of the diffstat for kernel/sched/core.c is shuffling the > PREEMPT_DYNAMIC code later in the file, and the actual additions are > fairly trivial. > > I've given this very light build+boot testing so far. > > Since v1 [1]: > * Rework Kconfig text to be clearer > * Rework arm64 entry code > * Clarify commit messages. > > Since v2 [2]: > * Add missing includes > * Always provide prototype for preempt_schedule() > * Always provide prototype for preempt_schedule_notrace() > * Fix __cond_resched() to default to disabled > * Fix might_resched() to default to disabled > * Clarify example in commit message
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Thanks!
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