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From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	linux-arm-kernel@lists.infradead.org, ardb@kernel.org,
	bp@alien8.de, catalin.marinas@arm.com,
	dave.hansen@linux.intel.com, james.morse@arm.com,
	joey.gouly@arm.com, juri.lelli@redhat.com,
	linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com,
	tglx@linutronix.de, valentin.schneider@arm.com, will@kernel.org
Subject: Re: [PATCH v4 0/7] arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys
Date: Thu, 17 Feb 2022 19:59:47 +0100	[thread overview]
Message-ID: <20220217185947.GE23216@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20220217135211.GA745330@lothringen>

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... :-)

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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	linux-arm-kernel@lists.infradead.org, ardb@kernel.org,
	bp@alien8.de, catalin.marinas@arm.com,
	dave.hansen@linux.intel.com, james.morse@arm.com,
	joey.gouly@arm.com, juri.lelli@redhat.com,
	linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com,
	tglx@linutronix.de, valentin.schneider@arm.com, will@kernel.org
Subject: Re: [PATCH v4 0/7] arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys
Date: Thu, 17 Feb 2022 19:59:47 +0100	[thread overview]
Message-ID: <20220217185947.GE23216@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20220217135211.GA745330@lothringen>

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... :-)

  reply	other threads:[~2022-02-17 19:01 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-14 16:52 [PATCH v4 0/7] arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys Mark Rutland
2022-02-14 16:52 ` Mark Rutland
2022-02-14 16:52 ` [PATCH v4 1/7] sched/preempt: move PREEMPT_DYNAMIC logic later Mark Rutland
2022-02-14 16:52   ` Mark Rutland
2022-02-19 10:21   ` [tip: sched/core] sched/preempt: Move " tip-bot2 for Mark Rutland
2022-02-14 16:52 ` [PATCH v4 2/7] sched/preempt: refactor sched_dynamic_update() Mark Rutland
2022-02-14 16:52   ` Mark Rutland
2022-02-19 10:21   ` [tip: sched/core] sched/preempt: Refactor sched_dynamic_update() tip-bot2 for Mark Rutland
2022-02-14 16:52 ` [PATCH v4 3/7] sched/preempt: simplify irqentry_exit_cond_resched() callers Mark Rutland
2022-02-14 16:52   ` Mark Rutland
2022-02-19 10:21   ` [tip: sched/core] sched/preempt: Simplify " tip-bot2 for Mark Rutland
2022-02-14 16:52 ` [PATCH v4 4/7] sched/preempt: decouple HAVE_PREEMPT_DYNAMIC from GENERIC_ENTRY Mark Rutland
2022-02-14 16:52   ` Mark Rutland
2022-02-19 10:21   ` [tip: sched/core] sched/preempt: Decouple " tip-bot2 for Mark Rutland
2022-02-14 16:52 ` [PATCH v4 5/7] sched/preempt: add PREEMPT_DYNAMIC using static keys Mark Rutland
2022-02-14 16:52   ` Mark Rutland
2022-02-19 10:21   ` [tip: sched/core] sched/preempt: Add " tip-bot2 for Mark Rutland
2022-03-18  8:49   ` [PATCH v4 5/7] sched/preempt: add " Sven Schnelle
2022-03-18  8:49     ` Sven Schnelle
2022-02-14 16:52 ` [PATCH v4 6/7] arm64: entry: centralize preemption decision Mark Rutland
2022-02-14 16:52   ` Mark Rutland
2022-02-19 10:21   ` [tip: sched/core] arm64: entry: Centralize " tip-bot2 for Mark Rutland
2022-02-14 16:52 ` [PATCH v4 7/7] arm64: support PREEMPT_DYNAMIC Mark Rutland
2022-02-14 16:52   ` Mark Rutland
2022-02-19 10:21   ` [tip: sched/core] arm64: Support PREEMPT_DYNAMIC tip-bot2 for Mark Rutland
2022-02-17 13:52 ` [PATCH v4 0/7] arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys Frederic Weisbecker
2022-02-17 13:52   ` Frederic Weisbecker
2022-02-17 18:59   ` Peter Zijlstra [this message]
2022-02-17 18:59     ` Peter Zijlstra

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