Message ID | 20220214165216.2231574-1-mark.rutland@arm.com (mailing list archive) |
---|---|
Headers | show |
Series | arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys | expand |
On Mon, Feb 14, 2022 at 04:52:09PM +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. Acked-by: Frederic Weisbecker <frederic@kernel.org> Thanks!
On Thu, Feb 17, 2022 at 02:52:11PM +0100, Frederic Weisbecker wrote: > On Mon, Feb 14, 2022 at 04:52:09PM +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. > > Acked-by: Frederic Weisbecker <frederic@kernel.org> I'll go stick them in sched/core then... :-)