| Message ID | 20220209153535.818830-1-mark.rutland@arm.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys | expand |
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!
On Wed, 9 Feb 2022 at 16:35, Mark Rutland <mark.rutland@arm.com> 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 > > [1] https://lore.kernel.org/r/20211109172408.49641-1-mark.rutland@arm.com/ > [2] https://lore.kernel.org/r/20220204150557.434610-1-mark.rutland@arm.com/ > > Mark Rutland (7): > sched/preempt: move PREEMPT_DYNAMIC logic later > sched/preempt: refactor sched_dynamic_update() > sched/preempt: simplify irqentry_exit_cond_resched() callers > sched/preempt: decouple HAVE_PREEMPT_DYNAMIC from GENERIC_ENTRY > sched/preempt: add PREEMPT_DYNAMIC using static keys > arm64: entry: centralize premeption decision > arm64: support PREEMPT_DYNAMIC > Acked-by: Ard Biesheuvel <ardb@kernel.org> > arch/Kconfig | 37 +++- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/preempt.h | 19 +- > arch/arm64/kernel/entry-common.c | 28 ++- > arch/x86/Kconfig | 2 +- > arch/x86/include/asm/preempt.h | 10 +- > include/linux/entry-common.h | 15 +- > include/linux/kernel.h | 7 +- > include/linux/sched.h | 10 +- > kernel/entry/common.c | 23 +- > kernel/sched/core.c | 347 ++++++++++++++++++------------- > 11 files changed, 327 insertions(+), 172 deletions(-) > > -- > 2.30.2 >