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barrier: Add smp_cond_load_*_timeout() #6159

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@kernel-patches-daemon-bpf-rc kernel-patches-daemon-bpf-rc bot commented Oct 16, 2025

Pull request for series with
subject: barrier: Add smp_cond_load_*_timeout()
version: 6
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1012471

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kernel-patches-daemon-bpf-rc bot commented Oct 16, 2025

Upstream branch: 48a97ff
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1012471
version: 6

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kernel-patches-review-bot bot commented Oct 16, 2025 

commit 4fa5fd242047bc2ad2d613d9826b0e074cdbe289
Author: Ankur Arora <[email protected]>

atomic: Add atomic_cond_read_*_timeout()

This patch adds atomic_cond_read_*_timeout() and
atomic64_cond_read_*_timeout() macros to provide atomic load wrappers
around the cond-load timeout interfaces.

> diff --git a/include/linux/atomic.h b/include/linux/atomic.h
> index 8dd57c3a9..b3f77a89e 100644
> --- a/include/linux/atomic.h
> +++ b/include/linux/atomic.h
> @@ -31,6 +31,14 @@
>  #define atomic64_cond_read_acquire(v, c) smp_cond_load_acquire(&(v)->counter, (c))
>  #define atomic64_cond_read_relaxed(v, c) smp_cond_load_relaxed(&(v)->counter, (c))
>
> +#define atomic_cond_read_acquire_timeout(v, c, t) \
> +	smp_cond_load_acquire_timeout(&(v)->counter, (c), (t))
> +#define atomic_cond_read_relaxed_timeout(v, c, t) \
> +	smp_cond_load_relaxed_timeout(&(v)->counter, (c), (t))
> +
> +#define atomic64_cond_read_acquire_timeout(v, c) smp_cond_load_acquire_timeout(&(v)->counter, (c))
> +#define atomic64_cond_read_relaxed_timeout(v, c) smp_cond_load_relaxed_timeout(&(v)->counter, (c))
                                                     ^^^^

Are the atomic64 timeout macros missing the timeout parameter?  The
atomic_cond_read_*_timeout macros correctly take three parameters (v, c, t),
but atomic64_cond_read_acquire_timeout and atomic64_cond_read_relaxed_timeout
only take two parameters (v, c).

The underlying smp_cond_load_*_timeout functions require three arguments:
(ptr, cond_expr, time_check_expr). With the current definitions, the
time_check_expr parameter will be undefined when these macros expand.

> +
>  /*
>   * The idea here is to build acquire/release variants by adding explicit
>   * barriers on top of the relaxed variant. In the case where the relaxed

AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

In-Reply-To-Subject: atomic: Add atomic_cond_read_*_timeout()
CI run summary: https://github.com/kernel-patches/bpf-rc/actions/runs/18568994458

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kernel-patches-daemon-bpf-rc bot commented Oct 16, 2025

Forwarding comment 3411999540 via email
In-Reply-To: [email protected]
Patch: https://patchwork.kernel.org/project/netdevbpf/patch/[email protected]/

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kernel-patches-daemon-bpf-rc bot commented Oct 16, 2025

Upstream branch: 48a97ff
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1012471
version: 6

@terminus
asm-generic: barrier: Add smp_cond_load_relaxed_timeout()
6d8c107 
Add smp_cond_load_relaxed_timeout(), which extends
smp_cond_load_relaxed() to allow waiting for a duration.

The waiting loop uses cpu_poll_relax() to wait on the condition
variable with a periodic evaluation of a time-check.

cpu_poll_relax() unless overridden by the arch code, amounts to
a cpu_relax().

The number of times we spin is defined by SMP_TIMEOUT_POLL_COUNT
(chosen to be 200 by default) which, assuming each cpu_poll_relax()
iteration takes around 20-30 cycles (measured on a variety of x86
platforms), for a total of ~4000-6000 cycles.

Cc: Arnd Bergmann <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: [email protected]
Reviewed-by: Catalin Marinas <[email protected]>
Reviewed-by: Haris Okanovic <[email protected]>
Tested-by: Haris Okanovic <[email protected]>
Signed-off-by: Ankur Arora <[email protected]>
@terminus
arm64: barrier: support smp_cond_load_relaxed_timeout()
6718946 
Support waiting in smp_cond_load_relaxed_timeout() via
__cmpwait_relaxed(). Limit this to when the event-stream is enabled,
to ensure that we wake from WFE periodically and don't block forever
if there are no stores to the cacheline.

In the unlikely event that the event-stream is unavailable, fallback
to spin-waiting.

Also set SMP_TIMEOUT_POLL_COUNT to 1 so we do the time-check for each
iteration in smp_cond_load_relaxed_timeout().

Cc: [email protected]
Cc: Catalin Marinas <[email protected]>
Suggested-by: Will Deacon <[email protected]>
Signed-off-by: Ankur Arora <[email protected]>
@terminus
arm64: rqspinlock: Remove private copy of smp_cond_load_acquire_timewait
83e87f8 
In preparation for defining smp_cond_load_acquire_timeout(), remove
the private copy. Lacking this, the rqspinlock code falls back to using
smp_cond_load_acquire().

Cc: Kumar Kartikeya Dwivedi <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Reviewed-by: Haris Okanovic <[email protected]>
Signed-off-by: Ankur Arora <[email protected]>
@terminus
asm-generic: barrier: Add smp_cond_load_acquire_timeout()
7baf042 
Add the acquire variant of smp_cond_load_relaxed_timeout(). This
reuses the relaxed variant, with an additional LOAD->LOAD
ordering.

Cc: Arnd Bergmann <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: [email protected]
Reviewed-by: Catalin Marinas <[email protected]>
Reviewed-by: Haris Okanovic <[email protected]>
Tested-by: Haris Okanovic <[email protected]>
Signed-off-by: Ankur Arora <[email protected]>
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kernel-patches-daemon-bpf-rc bot commented Oct 16, 2025

Upstream branch: 48a97ff
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1012471
version: 6

@terminus
atomic: Add atomic_cond_read_*_timeout()
1876a0f 
Add atomic_cond_read_*_timeout() and, atomic64_cond_read_*_timeout(),
to provide atomic load wrappers around the cond-load timeout interfaces.

Cc: Will Deacon <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Boqun Feng <[email protected]>
Signed-off-by: Ankur Arora <[email protected]>
@terminus
rqspinlock: use smp_cond_load_acquire_timeout()
27eaa30 
Switch out the conditional load interfaces used by rqspinlock
to atomic_cond_read_acquire_timeout() and,
smp_cond_read_acquire_timeout().

Both these handle the timeout and amortize as needed, so use
check_timeout() directly.

Also, when using spin-wait implementations, redefine SMP_TIMEOUT_POLL_COUNT
to be 16k to be similar to the spin-count used in RES_CHECK_TIMEOUT().

Cc: Kumar Kartikeya Dwivedi <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Signed-off-by: Ankur Arora <[email protected]>
@terminus
cpuidle/poll_state: poll via smp_cond_load_relaxed_timeout()
fe4d64a 
The inner loop in poll_idle() polls over the thread_info flags,
waiting to see if the thread has TIF_NEED_RESCHED set. The loop
exits once the condition is met, or if the poll time limit has
been exceeded.

To minimize the number of instructions executed in each iteration,
the time check is done only intermittently (once every
POLL_IDLE_RELAX_COUNT iterations). In addition, each loop iteration
executes cpu_relax() which on certain platforms provides a hint to
the pipeline that the loop busy-waits, allowing the processor to
reduce power consumption.

This is close to what smp_cond_load_relaxed_timeout() provides. So,
restructure the loop and fold the loop condition and the timeout check
in smp_cond_load_relaxed_timeout().

Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Daniel Lezcano <[email protected]>
Signed-off-by: Ankur Arora <[email protected]>
@kernel-patches-daemon-bpf-rc kernel-patches-daemon-bpf-rc bot deleted the series/1012471=>bpf-next branch October 19, 2025 13:27
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@terminus