sched_ext: Maintain an online cid mask in the scheduler arenagrafted

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 <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 259 insertions, 0 deletions

diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
new file mode 100644
index 000000000..21d822aee
--- /dev/null
+++ b/include/drm/drm_fixed.h
@@ -0,0 +1,259 @@
+/*
+ * Copyright 2009 Red Hat Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * Authors: Dave Airlie
+ *          Christian König
+ */
+#ifndef DRM_FIXED_H
+#define DRM_FIXED_H
+
+#include <linux/math64.h>
+#include <linux/types.h>
+#include <linux/wordpart.h>
+
+typedef union dfixed {
+	u32 full;
+} fixed20_12;
+
+
+#define dfixed_const(A) (u32)(((A) << 12))/*  + ((B + 0.000122)*4096)) */
+#define dfixed_const_half(A) (u32)(((A) << 12) + 2048)
+#define dfixed_const_666(A) (u32)(((A) << 12) + 2731)
+#define dfixed_const_8(A) (u32)(((A) << 12) + 3277)
+#define dfixed_mul(A, B) ((u64)((u64)(A).full * (B).full + 2048) >> 12)
+#define dfixed_init(A) { .full = dfixed_const((A)) }
+#define dfixed_init_half(A) { .full = dfixed_const_half((A)) }
+#define dfixed_trunc(A) ((A).full >> 12)
+#define dfixed_frac(A) ((A).full & ((1 << 12) - 1))
+
+static inline u32 dfixed_floor(fixed20_12 A)
+{
+	u32 non_frac = dfixed_trunc(A);
+
+	return dfixed_const(non_frac);
+}
+
+static inline u32 dfixed_ceil(fixed20_12 A)
+{
+	u32 non_frac = dfixed_trunc(A);
+
+	if (A.full > dfixed_const(non_frac))
+		return dfixed_const(non_frac + 1);
+	else
+		return dfixed_const(non_frac);
+}
+
+static inline u32 dfixed_div(fixed20_12 A, fixed20_12 B)
+{
+	u64 tmp = ((u64)A.full << 13);
+
+	do_div(tmp, B.full);
+	tmp += 1;
+	tmp /= 2;
+	return lower_32_bits(tmp);
+}
+
+#define DRM_FIXED_POINT		32
+#define DRM_FIXED_ONE		(1ULL << DRM_FIXED_POINT)
+#define DRM_FIXED_DECIMAL_MASK	(DRM_FIXED_ONE - 1)
+#define DRM_FIXED_DIGITS_MASK	(~DRM_FIXED_DECIMAL_MASK)
+#define DRM_FIXED_EPSILON	1LL
+#define DRM_FIXED_ALMOST_ONE	(DRM_FIXED_ONE - DRM_FIXED_EPSILON)
+
+/**
+ * drm_sm2fixp() - convert signed-magnitude to fixed point
+ * @a: 1.31.32 signed-magnitude fixed point
+ *
+ * Convert a 1.31.32 signed-magnitude fixed point to 32.32
+ * 2s-complement fixed point
+ *
+ * @return s64 2s-complement fixed point
+ */
+static inline s64 drm_sm2fixp(__u64 a)
+{
+	if ((a & (1LL << 63))) {
+		return -(a & 0x7fffffffffffffffll);
+	} else {
+		return a;
+	}
+}
+
+static inline s64 drm_int2fixp(int a)
+{
+	return ((s64)a) << DRM_FIXED_POINT;
+}
+
+static inline int drm_fixp2int(s64 a)
+{
+	return ((s64)a) >> DRM_FIXED_POINT;
+}
+
+static inline int drm_fixp2int_round(s64 a)
+{
+	return drm_fixp2int(a + DRM_FIXED_ONE / 2);
+}
+
+static inline int drm_fixp2int_ceil(s64 a)
+{
+	if (a >= 0)
+		return drm_fixp2int(a + DRM_FIXED_ALMOST_ONE);
+	else
+		return drm_fixp2int(a - DRM_FIXED_ALMOST_ONE);
+}
+
+static inline unsigned drm_fixp_msbset(s64 a)
+{
+	unsigned shift, sign = (a >> 63) & 1;
+
+	for (shift = 62; shift > 0; --shift)
+		if (((a >> shift) & 1) != sign)
+			return shift;
+
+	return 0;
+}
+
+static inline s64 drm_fixp_mul(s64 a, s64 b)
+{
+	unsigned shift = drm_fixp_msbset(a) + drm_fixp_msbset(b);
+	s64 result;
+
+	if (shift > 61) {
+		shift = shift - 61;
+		a >>= (shift >> 1) + (shift & 1);
+		b >>= shift >> 1;
+	} else
+		shift = 0;
+
+	result = a * b;
+
+	if (shift > DRM_FIXED_POINT)
+		return result << (shift - DRM_FIXED_POINT);
+
+	if (shift < DRM_FIXED_POINT)
+		return result >> (DRM_FIXED_POINT - shift);
+
+	return result;
+}
+
+static inline s64 drm_fixp_div(s64 a, s64 b)
+{
+	unsigned shift = 62 - drm_fixp_msbset(a);
+	s64 result;
+
+	a <<= shift;
+
+	if (shift < DRM_FIXED_POINT)
+		b >>= (DRM_FIXED_POINT - shift);
+
+	result = div64_s64(a, b);
+
+	if (shift > DRM_FIXED_POINT)
+		return result >> (shift - DRM_FIXED_POINT);
+
+	return result;
+}
+
+static inline s64 drm_fixp_from_fraction(s64 a, s64 b)
+{
+	s64 res;
+	bool a_neg = a < 0;
+	bool b_neg = b < 0;
+	u64 a_abs = a_neg ? -a : a;
+	u64 b_abs = b_neg ? -b : b;
+	u64 rem;
+
+	/* determine integer part */
+	u64 res_abs  = div64_u64_rem(a_abs, b_abs, &rem);
+
+	/* determine fractional part */
+	{
+		u32 i = DRM_FIXED_POINT;
+
+		do {
+			rem <<= 1;
+			res_abs <<= 1;
+			if (rem >= b_abs) {
+				res_abs |= 1;
+				rem -= b_abs;
+			}
+		} while (--i != 0);
+	}
+
+	/* round up LSB */
+	{
+		u64 summand = (rem << 1) >= b_abs;
+
+		res_abs += summand;
+	}
+
+	res = (s64) res_abs;
+	if (a_neg ^ b_neg)
+		res = -res;
+	return res;
+}
+
+static inline s64 drm_fixp_exp(s64 x)
+{
+	s64 tolerance = div64_s64(DRM_FIXED_ONE, 1000000);
+	s64 sum = DRM_FIXED_ONE, term, y = x;
+	u64 count = 1;
+
+	if (x < 0)
+		y = -1 * x;
+
+	term = y;
+
+	while (term >= tolerance) {
+		sum = sum + term;
+		count = count + 1;
+		term = drm_fixp_mul(term, div64_s64(y, count));
+	}
+
+	if (x < 0)
+		sum = drm_fixp_div(DRM_FIXED_ONE, sum);
+
+	return sum;
+}
+
+static inline int fxp_q4_from_int(int val_int)
+{
+	return val_int << 4;
+}
+
+static inline int fxp_q4_to_int(int val_q4)
+{
+	return val_q4 >> 4;
+}
+
+static inline int fxp_q4_to_int_roundup(int val_q4)
+{
+	return (val_q4 + 0xf) >> 4;
+}
+
+static inline int fxp_q4_to_frac(int val_q4)
+{
+	return val_q4 & 0xf;
+}
+
+#define FXP_Q4_FMT		"%d.%04d"
+#define FXP_Q4_ARGS(val_q4)	fxp_q4_to_int(val_q4), (fxp_q4_to_frac(val_q4) * 625)
+
+#endif