2014-04-11 13:55:57

by Peter Zijlstra

Subject: [RFC][PATCH 1/8] sched,idle,alpha: 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.

Cc: Thomas Gleixner <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Richard Henderson <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
---
arch/alpha/include/asm/thread_info.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/alpha/include/asm/thread_info.h
+++ b/arch/alpha/include/asm/thread_info.h
@@ -73,12 +73,14 @@ register struct thread_info *__current_t
#define TIF_SYSCALL_AUDIT 4 /* syscall audit active */
#define TIF_DIE_IF_KERNEL 9 /* dik recursion lock */
#define TIF_MEMDIE 13 /* is terminating due to OOM killer */
+#define TIF_POLLING_NRFLAG 14 /* idle is polling for TIF_NEED_RESCHED */

#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
#define _TIF_SIGPENDING (1<<TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
#define _TIF_SYSCALL_AUDIT (1<<TIF_SYSCALL_AUDIT)
+#define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG)

/* Work to do on interrupt/exception return. */
#define _TIF_WORK_MASK (_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
@@ -92,8 +94,6 @@ register struct thread_info *__current_t
#define TS_UAC_NOFIX 0x0002 /* ! flags as they match */
#define TS_UAC_SIGBUS 0x0004 /* ! userspace part of 'osf_sysinfo' */
#define TS_RESTORE_SIGMASK 0x0008 /* restore signal mask in do_signal() */
-#define TS_POLLING 0x0010 /* idle task polling need_resched,
- skip sending interrupt */

#ifndef __ASSEMBLY__
#define HAVE_SET_RESTORE_SIGMASK 1

2014-04-11 14:38:31

by Richard Henderson

Subject: Re: [RFC][PATCH 1/8] sched,idle,alpha: Switch from TS_POLLING to TIF_POLLING_NRFLAG

On 04/11/2014 06:42 AM, Peter Zijlstra wrote:
> 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.
>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Andy Lutomirski <[email protected]>
> Cc: Richard Henderson <[email protected]>
> Signed-off-by: Peter Zijlstra <[email protected]>
> ---
> arch/alpha/include/asm/thread_info.h | 4 ++--
> 1 file changed, 2 inser

Acked-by: Richard Henderson <[email protected]>


r~