From a9e3760b0838299649c0d57cca44daaf40ba3c33 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 14 Sep 2026 22:12:34 -1000 Subject: sched_ext: Maintain an online cid mask in the scheduler arena Schedulers on the default cid mapping treat [0, nr_online_cids) as the online set and restart on hotplug. Schedulers that install their own mapping with scx_bpf_cid_override() have no way to learn which cids are online: the count no longer identifies members and the CPU-form cpumask is unusable from cid programs. This is an obvious hole in the cid API. Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's arena, allocated alongside the per-CPU scratch masks and populated after the cid mapping is finalized and before ops.init(), for child schedulers too. The pointer stays valid through ops.exit() with no reference to take. It is the arena offset as a void pointer, the same form struct_ops arena arguments arrive in. The verifier types the void return as a scalar for the program's arena cast. The mask follows the SCX hotplug notifications: seeded from cpu_active_mask and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask only inside a hotplug transition. Updates walk the scheduler list under the lock that also serializes unlinking. Reads are live, not atomic snapshots. Root initialization excludes hotplug. v2: Reworded the getter kerneldoc (Andrea Righi). Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- lib/math/div64.c | 333 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 333 insertions(+) create mode 100644 lib/math/div64.c (limited to 'lib/math/div64.c') diff --git a/lib/math/div64.c b/lib/math/div64.c new file mode 100644 index 000000000..d1e92ea24 --- /dev/null +++ b/lib/math/div64.c @@ -0,0 +1,333 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2003 Bernardo Innocenti + * + * Based on former do_div() implementation from asm-parisc/div64.h: + * Copyright (C) 1999 Hewlett-Packard Co + * Copyright (C) 1999 David Mosberger-Tang + * + * + * Generic C version of 64bit/32bit division and modulo, with + * 64bit result and 32bit remainder. + * + * The fast case for (n>>32 == 0) is handled inline by do_div(). + * + * Code generated for this function might be very inefficient + * for some CPUs. __div64_32() can be overridden by linking arch-specific + * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S + * or by defining a preprocessor macro in arch/include/asm/div64.h. + */ + +#include +#include +#include +#include +#include +#include + +/* Not needed on 64bit architectures */ +#if BITS_PER_LONG == 32 + +#ifndef __div64_32 +uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base) +{ + uint64_t rem = *n; + uint64_t b = base; + uint64_t res, d = 1; + uint32_t high = rem >> 32; + + /* Reduce the thing a bit first */ + res = 0; + if (high >= base) { + high /= base; + res = (uint64_t) high << 32; + rem -= (uint64_t) (high*base) << 32; + } + + while ((int64_t)b > 0 && b < rem) { + b = b+b; + d = d+d; + } + + do { + if (rem >= b) { + rem -= b; + res += d; + } + b >>= 1; + d >>= 1; + } while (d); + + *n = res; + return rem; +} +EXPORT_SYMBOL(__div64_32); +#endif + +#ifndef div_s64_rem +s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder) +{ + u64 quotient; + + if (dividend < 0) { + quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder); + *remainder = -*remainder; + if (divisor > 0) + quotient = -quotient; + } else { + quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder); + if (divisor < 0) + quotient = -quotient; + } + return quotient; +} +EXPORT_SYMBOL(div_s64_rem); +#endif + +/* + * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder + * @dividend: 64bit dividend + * @divisor: 64bit divisor + * @remainder: 64bit remainder + * + * This implementation is a comparable to algorithm used by div64_u64. + * But this operation, which includes math for calculating the remainder, + * is kept distinct to avoid slowing down the div64_u64 operation on 32bit + * systems. + */ +#ifndef div64_u64_rem +u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder) +{ + u32 high = divisor >> 32; + u64 quot; + + if (high == 0) { + u32 rem32; + quot = div_u64_rem(dividend, divisor, &rem32); + *remainder = rem32; + } else { + int n = fls(high); + quot = div_u64(dividend >> n, divisor >> n); + + if (quot != 0) + quot--; + + *remainder = dividend - quot * divisor; + if (*remainder >= divisor) { + quot++; + *remainder -= divisor; + } + } + + return quot; +} +EXPORT_SYMBOL(div64_u64_rem); +#endif + +/* + * div64_u64 - unsigned 64bit divide with 64bit divisor + * @dividend: 64bit dividend + * @divisor: 64bit divisor + * + * This implementation is a modified version of the algorithm proposed + * by the book 'Hacker's Delight'. The original source and full proof + * can be found here and is available for use without restriction. + * + * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt' + */ +#ifndef div64_u64 +u64 div64_u64(u64 dividend, u64 divisor) +{ + u32 high = divisor >> 32; + u64 quot; + + if (high == 0) { + quot = div_u64(dividend, divisor); + } else { + int n = fls(high); + quot = div_u64(dividend >> n, divisor >> n); + + if (quot != 0) + quot--; + if ((dividend - quot * divisor) >= divisor) + quot++; + } + + return quot; +} +EXPORT_SYMBOL(div64_u64); +#endif + +#ifndef div64_s64 +s64 div64_s64(s64 dividend, s64 divisor) +{ + s64 quot, t; + + quot = div64_u64(abs(dividend), abs(divisor)); + t = (dividend ^ divisor) >> 63; + + return (quot ^ t) - t; +} +EXPORT_SYMBOL(div64_s64); +#endif + +#endif /* BITS_PER_LONG == 32 */ + +/* + * Iterative div/mod for use when dividend is not expected to be much + * bigger than divisor. + */ +#ifndef iter_div_u64_rem +u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) +{ + return __iter_div_u64_rem(dividend, divisor, remainder); +} +EXPORT_SYMBOL(iter_div_u64_rem); +#endif + +#if !defined(mul_u64_add_u64_div_u64) || defined(test_mul_u64_add_u64_div_u64) + +#define mul_add(a, b, c) add_u64_u32(mul_u32_u32(a, b), c) + +#if defined(__SIZEOF_INT128__) && !defined(test_mul_u64_add_u64_div_u64) +static inline u64 mul_u64_u64_add_u64(u64 *p_lo, u64 a, u64 b, u64 c) +{ + /* native 64x64=128 bits multiplication */ + u128 prod = (u128)a * b + c; + + *p_lo = prod; + return prod >> 64; +} +#else +static inline u64 mul_u64_u64_add_u64(u64 *p_lo, u64 a, u64 b, u64 c) +{ + /* perform a 64x64=128 bits multiplication in 32bit chunks */ + u64 x, y, z; + + /* Since (x-1)(x-1) + 2(x-1) == x.x - 1 two u32 can be added to a u64 */ + x = mul_add(a, b, c); + y = mul_add(a, b >> 32, c >> 32); + y = add_u64_u32(y, x >> 32); + z = mul_add(a >> 32, b >> 32, y >> 32); + y = mul_add(a >> 32, b, y); + *p_lo = (y << 32) + (u32)x; + return add_u64_u32(z, y >> 32); +} +#endif + +#ifndef BITS_PER_ITER +#define BITS_PER_ITER (__LONG_WIDTH__ >= 64 ? 32 : 16) +#endif + +#if BITS_PER_ITER == 32 +#define mul_u64_long_add_u64(p_lo, a, b, c) mul_u64_u64_add_u64(p_lo, a, b, c) +#define add_u64_long(a, b) ((a) + (b)) +#else +#undef BITS_PER_ITER +#define BITS_PER_ITER 16 +static inline u32 mul_u64_long_add_u64(u64 *p_lo, u64 a, u32 b, u64 c) +{ + u64 n_lo = mul_add(a, b, c); + u64 n_med = mul_add(a >> 32, b, c >> 32); + + n_med = add_u64_u32(n_med, n_lo >> 32); + *p_lo = n_med << 32 | (u32)n_lo; + return n_med >> 32; +} + +#define add_u64_long(a, b) add_u64_u32(a, b) +#endif + +u64 mul_u64_add_u64_div_u64(u64 a, u64 b, u64 c, u64 d) +{ + unsigned long d_msig, q_digit; + unsigned int reps, d_z_hi; + u64 quotient, n_lo, n_hi; + u32 overflow; + + n_hi = mul_u64_u64_add_u64(&n_lo, a, b, c); + + if (!n_hi) + return div64_u64(n_lo, d); + + if (unlikely(n_hi >= d)) { + /* trigger runtime exception if divisor is zero */ + if (d == 0) { + unsigned long zero = 0; + + OPTIMIZER_HIDE_VAR(zero); + return ~0UL/zero; + } + /* overflow: result is unrepresentable in a u64 */ + return ~0ULL; + } + + /* Left align the divisor, shifting the dividend to match */ + d_z_hi = __builtin_clzll(d); + if (d_z_hi) { + d <<= d_z_hi; + n_hi = n_hi << d_z_hi | n_lo >> (64 - d_z_hi); + n_lo <<= d_z_hi; + } + + reps = 64 / BITS_PER_ITER; + /* Optimise loop count for small dividends */ + if (!(u32)(n_hi >> 32)) { + reps -= 32 / BITS_PER_ITER; + n_hi = n_hi << 32 | n_lo >> 32; + n_lo <<= 32; + } +#if BITS_PER_ITER == 16 + if (!(u32)(n_hi >> 48)) { + reps--; + n_hi = add_u64_u32(n_hi << 16, n_lo >> 48); + n_lo <<= 16; + } +#endif + + /* Invert the dividend so we can use add instead of subtract. */ + n_lo = ~n_lo; + n_hi = ~n_hi; + + /* + * Get the most significant BITS_PER_ITER bits of the divisor. + * This is used to get a low 'guestimate' of the quotient digit. + */ + d_msig = (d >> (64 - BITS_PER_ITER)) + 1; + + /* + * Now do a 'long division' with BITS_PER_ITER bit 'digits'. + * The 'guess' quotient digit can be low and BITS_PER_ITER+1 bits. + * The worst case is dividing ~0 by 0x8000 which requires two subtracts. + */ + quotient = 0; + while (reps--) { + q_digit = (unsigned long)(~n_hi >> (64 - 2 * BITS_PER_ITER)) / d_msig; + /* Shift 'n' left to align with the product q_digit * d */ + overflow = n_hi >> (64 - BITS_PER_ITER); + n_hi = add_u64_u32(n_hi << BITS_PER_ITER, n_lo >> (64 - BITS_PER_ITER)); + n_lo <<= BITS_PER_ITER; + /* Add product to negated divisor */ + overflow += mul_u64_long_add_u64(&n_hi, d, q_digit, n_hi); + /* Adjust for the q_digit 'guestimate' being low */ + while (overflow < 0xffffffff >> (32 - BITS_PER_ITER)) { + q_digit++; + n_hi += d; + overflow += n_hi < d; + } + quotient = add_u64_long(quotient << BITS_PER_ITER, q_digit); + } + + /* + * The above only ensures the remainder doesn't overflow, + * it can still be possible to add (aka subtract) another copy + * of the divisor. + */ + if ((n_hi + d) > n_hi) + quotient++; + return quotient; +} +#if !defined(test_mul_u64_add_u64_div_u64) +EXPORT_SYMBOL(mul_u64_add_u64_div_u64); +#endif +#endif -- cgit v1.3.1