linux-kernel - [tip:sched/core] sched/idle, x86: Switch from TS_POLLING to TIF_POLLING

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Message-ID: <tip-7yksmqtlv4nfowmlqr1rifoi@git.kernel.org>
Date:	Thu, 8 May 2014 03:46:50 -0700
From:	tip-bot for Peter Zijlstra <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	jkosina@...e.cz, luto@...capital.net, srostedt@...hat.com,
	tglx@...utronix.de, oleg@...hat.com
Subject: [tip:sched/core] sched/idle, x86:
  Switch from TS_POLLING to TIF_POLLING_NRFLAG

Commit-ID:  f80c5b39b80ab4d52acd940c03b89948cafdbd18
Gitweb:     http://git.kernel.org/tip/f80c5b39b80ab4d52acd940c03b89948cafdbd18
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Fri, 11 Apr 2014 09:59:05 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 8 May 2014 09:16:56 +0200

sched/idle, x86: Switch from TS_POLLING to TIF_POLLING_NRFLAG

Standardize the idle polling indicator to TIF_POLLING_NRFLAG such that
both TIF_NEED_RESCHED and TIF_POLLING_NRFLAG are in the same word.
This will allow us, using fetch_or(), to both set NEED_RESCHED and
check for POLLING_NRFLAG in a single operation and avoid pointless
wakeups.

Changing from the non-atomic thread_info::status flags to the atomic
thread_info::flags shouldn't be a big issue since most polling state
changes were followed/preceded by a full memory barrier anyway.

Also, fix up the apm_32 idle function, clearly that was forgotten in
the last conversion. The default idle state is !POLLING so just kill
the lot.

Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Steven Rostedt <srostedt@...hat.com>
Link: http://lkml.kernel.org/n/tip-7yksmqtlv4nfowmlqr1rifoi@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/thread_info.h |  4 ++--
 arch/x86/kernel/apm_32.c           | 11 -----------
 2 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 47e5de2..8540538 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -83,6 +83,7 @@ struct thread_info {
 #define TIF_FORK		18	/* ret_from_fork */
 #define TIF_NOHZ		19	/* in adaptive nohz mode */
 #define TIF_MEMDIE		20	/* is terminating due to OOM killer */
+#define TIF_POLLING_NRFLAG	21	/* idle is polling for TIF_NEED_RESCHED */
 #define TIF_IO_BITMAP		22	/* uses I/O bitmap */
 #define TIF_FORCED_TF		24	/* true if TF in eflags artificially */
 #define TIF_BLOCKSTEP		25	/* set when we want DEBUGCTLMSR_BTF */
@@ -106,6 +107,7 @@ struct thread_info {
 #define _TIF_IA32		(1 << TIF_IA32)
 #define _TIF_FORK		(1 << TIF_FORK)
 #define _TIF_NOHZ		(1 << TIF_NOHZ)
+#define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_IO_BITMAP		(1 << TIF_IO_BITMAP)
 #define _TIF_FORCED_TF		(1 << TIF_FORCED_TF)
 #define _TIF_BLOCKSTEP		(1 << TIF_BLOCKSTEP)
@@ -191,8 +193,6 @@ static inline struct thread_info *current_thread_info(void)
  * have to worry about atomic accesses.
  */
 #define TS_COMPAT		0x0002	/* 32bit syscall active (64BIT)*/
-#define TS_POLLING		0x0004	/* idle task polling need_resched,
-					   skip sending interrupt */
 #define TS_RESTORE_SIGMASK	0x0008	/* restore signal mask in do_signal() */
 
 #ifndef __ASSEMBLY__
diff --git a/arch/x86/kernel/apm_32.c b/arch/x86/kernel/apm_32.c
index 3ab0343..f3a1f04 100644
--- a/arch/x86/kernel/apm_32.c
+++ b/arch/x86/kernel/apm_32.c
@@ -844,21 +844,10 @@ static int apm_do_idle(void)
 	int polling;
 	int err = 0;
 
-	polling = !!(current_thread_info()->status & TS_POLLING);
-	if (polling) {
-		current_thread_info()->status &= ~TS_POLLING;
-		/*
-		 * TS_POLLING-cleared state must be visible before we
-		 * test NEED_RESCHED:
-		 */
-		smp_mb();
-	}
 	if (!need_resched()) {
 		idled = 1;
 		ret = apm_bios_call_simple(APM_FUNC_IDLE, 0, 0, &eax, &err);
 	}
-	if (polling)
-		current_thread_info()->status |= TS_POLLING;
 
 	if (!idled)
 		return 0;
--
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