linux-kernel - [PATCH 2/6] sched: avoid using ilog2() in sched.h

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Date: Mon, 27 May 2024 17:56:44 -0700
From: Yury Norov <yury.norov@...il.com>
To: linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-mm@...ck.org,
	rcu@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Cc: Yury Norov <yury.norov@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Amit Daniel Kachhap <amit.kachhap@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Christoph Lameter <cl@...ux.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Dennis Zhou <dennis@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Zefan Li <lizefan.x@...edance.com>
Subject: [PATCH 2/6] sched: avoid using ilog2() in sched.h

<linux/sched.h> indirectly via cpumask.h path includes the ilog2.h header
to calculate ilog2(TASK_REPORT_MAX). The following patches drops sched.h
dependency on cpumask.h, and to have a successful build, the header has
to be included explicitly.

sched.h is a frequently included header, and it's better to keep the
dependency list as small as possible. So, instead of including ilog2.h
for a single BUILD_BUG_ON() check, the same check may be implemented by
taking exponent of the other part of equation.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 include/linux/sched.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 61591ac6eab6..98abb07de149 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1604,7 +1604,7 @@ static inline char task_index_to_char(unsigned int state)
 {
 	static const char state_char[] = "RSDTtXZPI";
 
-	BUILD_BUG_ON(1 + ilog2(TASK_REPORT_MAX) != sizeof(state_char) - 1);
+	BUILD_BUG_ON(TASK_REPORT_MAX * 2 != 1 << (sizeof(state_char) - 1));
 
 	return state_char[state];
 }
-- 
2.40.1