* [PATCH 2/2] Revert "lib/sort.c: add _nonatomic() variants with cond_resched()"
2026-07-30 18:12 [PATCH 0/2] lib/sort: Clean up sort_nonatomic() and sort_r_nonatomic() Kuan-Wei Chiu
2026-07-30 18:12 ` [PATCH 1/2] iommu/arm-smmu-v3: Replace sort_nonatomic() with sort() Kuan-Wei Chiu
@ 2026-07-30 18:12 ` Kuan-Wei Chiu
2026-07-30 19:32 ` [PATCH 0/2] lib/sort: Clean up sort_nonatomic() and sort_r_nonatomic() Kuan-Wei Chiu
2 siblings, 0 replies; 4+ messages in thread
From: Kuan-Wei Chiu @ 2026-07-30 18:12 UTC (permalink / raw)
To: will, joro, akpm
Cc: robin.murphy, nicolinc, cychu, hhchung, amitamishra, marscheng,
linux-arm-kernel, iommu, linux-kernel, jserv, eleanor15x,
Kuan-Wei Chiu
This reverts commit e2a33a2a3258794891cdd6ca4b1318da6594d157.
After replacing the only in-tree user of sort_nonatomic() in the
arm-smmu-v3 driver with the standard sort(), the _nonatomic() variants
are no longer used anywhere in the kernel.
Remove sort_nonatomic() and sort_r_nonatomic() to clean up dead code.
This effectively drops the wrapper function __sort_r() and eliminates
the may_schedule branch and cond_resched() call from the inner loop of
the core sorting routine, slightly simplifying and optimizing the code.
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
include/linux/sort.h | 11 -----
lib/sort.c | 110 ++++++++++++-------------------------------
2 files changed, 31 insertions(+), 90 deletions(-)
diff --git a/include/linux/sort.h b/include/linux/sort.h
index c01ef804a0eb..871775978af0 100644
--- a/include/linux/sort.h
+++ b/include/linux/sort.h
@@ -23,15 +23,4 @@ void sort(void *base, size_t num, size_t size,
cmp_func_t cmp_func,
swap_func_t swap_func);
-/* Versions that periodically call cond_resched(): */
-
-void sort_r_nonatomic(void *base, size_t num, size_t size,
- cmp_r_func_t cmp_func,
- swap_r_func_t swap_func,
- const void *priv);
-
-void sort_nonatomic(void *base, size_t num, size_t size,
- cmp_func_t cmp_func,
- swap_func_t swap_func);
-
#endif
diff --git a/lib/sort.c b/lib/sort.c
index 52363995ccc5..8e73dc55476b 100644
--- a/lib/sort.c
+++ b/lib/sort.c
@@ -186,13 +186,36 @@ static size_t parent(size_t i, unsigned int lsbit, size_t size)
return i / 2;
}
-#include <linux/sched.h>
-
-static void __sort_r(void *base, size_t num, size_t size,
- cmp_r_func_t cmp_func,
- swap_r_func_t swap_func,
- const void *priv,
- bool may_schedule)
+/**
+ * sort_r - sort an array of elements
+ * @base: pointer to data to sort
+ * @num: number of elements
+ * @size: size of each element
+ * @cmp_func: pointer to comparison function
+ * @swap_func: pointer to swap function or NULL
+ * @priv: third argument passed to comparison function
+ *
+ * This function does a heapsort on the given array. You may provide
+ * a swap_func function if you need to do something more than a memory
+ * copy (e.g. fix up pointers or auxiliary data), but the built-in swap
+ * avoids a slow retpoline and so is significantly faster.
+ *
+ * The comparison function must adhere to specific mathematical
+ * properties to ensure correct and stable sorting:
+ * - Antisymmetry: cmp_func(a, b) must return the opposite sign of
+ * cmp_func(b, a).
+ * - Transitivity: if cmp_func(a, b) <= 0 and cmp_func(b, c) <= 0, then
+ * cmp_func(a, c) <= 0.
+ *
+ * Sorting time is O(n log n) both on average and worst-case. While
+ * quicksort is slightly faster on average, it suffers from exploitable
+ * O(n*n) worst-case behavior and extra memory requirements that make
+ * it less suitable for kernel use.
+ */
+void sort_r(void *base, size_t num, size_t size,
+ cmp_r_func_t cmp_func,
+ swap_r_func_t swap_func,
+ const void *priv)
{
/* pre-scale counters for performance */
size_t n = num * size, a = (num/2) * size;
@@ -263,9 +286,6 @@ static void __sort_r(void *base, size_t num, size_t size,
b = parent(b, lsbit, size);
do_swap(base + b, base + c, size, swap_func, priv);
}
-
- if (may_schedule)
- cond_resched();
}
n -= size;
@@ -273,63 +293,8 @@ static void __sort_r(void *base, size_t num, size_t size,
if (n == size * 2 && do_cmp(base, base + size, cmp_func, priv) > 0)
do_swap(base, base + size, size, swap_func, priv);
}
-
-/**
- * sort_r - sort an array of elements
- * @base: pointer to data to sort
- * @num: number of elements
- * @size: size of each element
- * @cmp_func: pointer to comparison function
- * @swap_func: pointer to swap function or NULL
- * @priv: third argument passed to comparison function
- *
- * This function does a heapsort on the given array. You may provide
- * a swap_func function if you need to do something more than a memory
- * copy (e.g. fix up pointers or auxiliary data), but the built-in swap
- * avoids a slow retpoline and so is significantly faster.
- *
- * The comparison function must adhere to specific mathematical
- * properties to ensure correct and stable sorting:
- * - Antisymmetry: cmp_func(a, b) must return the opposite sign of
- * cmp_func(b, a).
- * - Transitivity: if cmp_func(a, b) <= 0 and cmp_func(b, c) <= 0, then
- * cmp_func(a, c) <= 0.
- *
- * Sorting time is O(n log n) both on average and worst-case. While
- * quicksort is slightly faster on average, it suffers from exploitable
- * O(n*n) worst-case behavior and extra memory requirements that make
- * it less suitable for kernel use.
- */
-void sort_r(void *base, size_t num, size_t size,
- cmp_r_func_t cmp_func,
- swap_r_func_t swap_func,
- const void *priv)
-{
- __sort_r(base, num, size, cmp_func, swap_func, priv, false);
-}
EXPORT_SYMBOL(sort_r);
-/**
- * sort_r_nonatomic - sort an array of elements, with cond_resched
- * @base: pointer to data to sort
- * @num: number of elements
- * @size: size of each element
- * @cmp_func: pointer to comparison function
- * @swap_func: pointer to swap function or NULL
- * @priv: third argument passed to comparison function
- *
- * Same as sort_r, but preferred for larger arrays as it does a periodic
- * cond_resched().
- */
-void sort_r_nonatomic(void *base, size_t num, size_t size,
- cmp_r_func_t cmp_func,
- swap_r_func_t swap_func,
- const void *priv)
-{
- __sort_r(base, num, size, cmp_func, swap_func, priv, true);
-}
-EXPORT_SYMBOL(sort_r_nonatomic);
-
void sort(void *base, size_t num, size_t size,
cmp_func_t cmp_func,
swap_func_t swap_func)
@@ -339,19 +304,6 @@ void sort(void *base, size_t num, size_t size,
.swap = swap_func,
};
- return __sort_r(base, num, size, _CMP_WRAPPER, SWAP_WRAPPER, &w, false);
+ return sort_r(base, num, size, _CMP_WRAPPER, SWAP_WRAPPER, &w);
}
EXPORT_SYMBOL(sort);
-
-void sort_nonatomic(void *base, size_t num, size_t size,
- cmp_func_t cmp_func,
- swap_func_t swap_func)
-{
- struct wrapper w = {
- .cmp = cmp_func,
- .swap = swap_func,
- };
-
- return __sort_r(base, num, size, _CMP_WRAPPER, SWAP_WRAPPER, &w, true);
-}
-EXPORT_SYMBOL(sort_nonatomic);
--
2.55.0.508.g3f0d502094-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH 0/2] lib/sort: Clean up sort_nonatomic() and sort_r_nonatomic()
2026-07-30 18:12 [PATCH 0/2] lib/sort: Clean up sort_nonatomic() and sort_r_nonatomic() Kuan-Wei Chiu
2026-07-30 18:12 ` [PATCH 1/2] iommu/arm-smmu-v3: Replace sort_nonatomic() with sort() Kuan-Wei Chiu
2026-07-30 18:12 ` [PATCH 2/2] Revert "lib/sort.c: add _nonatomic() variants with cond_resched()" Kuan-Wei Chiu
@ 2026-07-30 19:32 ` Kuan-Wei Chiu
2 siblings, 0 replies; 4+ messages in thread
From: Kuan-Wei Chiu @ 2026-07-30 19:32 UTC (permalink / raw)
To: will, joro, akpm
Cc: robin.murphy, nicolinc, cychu, hhchung, amitamishra, marscheng,
linux-arm-kernel, iommu, linux-kernel, jserv, eleanor15x, kpsingh,
mattbobrowski, song, jolsa, ast, daniel, andrii, eddyz87, memxor,
martin.lau, yonghong.song, emil, rostedt, mhiramat,
mathieu.desnoyers, bpf, linux-trace-kernel
+Cc maintainers/reviewers of kernel/trace/bpf_trace.c
On Thu, Jul 30, 2026 at 06:12:14PM +0000, Kuan-Wei Chiu wrote:
> Remove the sort_nonatomic() and sort_r_nonatomic() APIs from the kernel
> library.
>
> Currently, the arm-smmu-v3 driver is the sole in-tree user of
> sort_nonatomic(). Because the array size being sorted is small in
I just realized that I missed another in-tree user: sort_r_nonatomic()
is actually being used in kernel/trace/bpf_trace.c.
Looking at the bpf code, the array size there is bounded by
MAX_TRACING_MULTI_CNT, which is set to (1u << 20). I guess sorting an
array of this size in a single go could potentially cause scheduling
latency spikes on certain configurations if we don't yield the cpu.
Because of this, it seems my proposal to completely remove
sort_r_nonatomic() and sort_nonatomic() from the core library was
premature.
Please let me know if you think otherwise, or if there is any
alternative approach for check_dup_ids() that would allow us to safely
drop sort_r_nonatomic(). Otherwise, please disregard this series.
Regards,
Kuan-Wei
> practice, there is no real risk of triggering a soft lockup. Therefore,
> the periodic cond_resched() calls provided by the _nonatomic variant
> are unnecessary.
>
> With the only in-tree user updated, the _nonatomic APIs are no longer
> needed anywhere in the kernel. Removing them effectively drops the
> wrapper function and eliminates the may_schedule branch from the
> innermost loop of the core sorting logic, slightly simplifying the code.
>
> Kuan-Wei Chiu (2):
> iommu/arm-smmu-v3: Replace sort_nonatomic() with sort()
> Revert "lib/sort.c: add _nonatomic() variants with cond_resched()"
>
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 6 +-
> include/linux/sort.h | 11 --
> lib/sort.c | 110 ++++++--------------
> 3 files changed, 34 insertions(+), 93 deletions(-)
>
> --
> 2.55.0.508.g3f0d502094-goog
>
^ permalink raw reply [flat|nested] 4+ messages in thread