Messages in this thread | | | From | Ankur Arora <> | Subject | Re: [PATCH 17/30] x86/thread_info: define TIF_NEED_RESCHED_LAZY | Date | Wed, 14 Feb 2024 12:31:29 -0800 |
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Mark Rutland <mark.rutland@arm.com> writes:
> Hi Ankur, > > On Mon, Feb 12, 2024 at 09:55:41PM -0800, Ankur Arora wrote: >> Define TIF_NEED_RESCHED_LAZY which, with TIF_NEED_RESCHED provides the >> scheduler with two kinds of rescheduling intent: TIF_NEED_RESCHED, >> for the usual rescheduling at the next safe preemption point; >> TIF_NEED_RESCHED_LAZY expressing an intent to reschedule at some >> time in the future while allowing the current task to run to >> completion. >> >> Cc: Ingo Molnar <mingo@redhat.com> >> Cc: Borislav Petkov <bp@alien8.de> >> Cc: Dave Hansen <dave.hansen@linux.intel.com> >> Originally-by: Thomas Gleixner <tglx@linutronix.de> >> Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/ >> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com> >> --- >> arch/x86/Kconfig | 1 + >> arch/x86/include/asm/thread_info.h | 10 ++++++++-- >> 2 files changed, 9 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >> index 5edec175b9bf..ab58558068a4 100644 >> --- a/arch/x86/Kconfig >> +++ b/arch/x86/Kconfig >> @@ -275,6 +275,7 @@ config X86 >> select HAVE_STATIC_CALL >> select HAVE_STATIC_CALL_INLINE if HAVE_OBJTOOL >> select HAVE_PREEMPT_DYNAMIC_CALL >> + select HAVE_PREEMPT_AUTO >> select HAVE_RSEQ >> select HAVE_RUST if X86_64 >> select HAVE_SYSCALL_TRACEPOINTS >> diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h >> index d63b02940747..88c1802185fc 100644 >> --- a/arch/x86/include/asm/thread_info.h >> +++ b/arch/x86/include/asm/thread_info.h >> @@ -81,8 +81,11 @@ struct thread_info { >> #define TIF_NOTIFY_RESUME 1 /* callback before returning to user */ >> #define TIF_SIGPENDING 2 /* signal pending */ >> #define TIF_NEED_RESCHED 3 /* rescheduling necessary */ >> -#define TIF_SINGLESTEP 4 /* reenable singlestep on user return*/ >> -#define TIF_SSBD 5 /* Speculative store bypass disable */ >> +#ifdef CONFIG_PREEMPT_AUTO >> +#define TIF_NEED_RESCHED_LAZY 4 /* Lazy rescheduling */ >> +#endif >> +#define TIF_SINGLESTEP 5 /* reenable singlestep on user return*/ >> +#define TIF_SSBD 6 /* Speculative store bypass disable */ > > It's a bit awkward/ugly to conditionally define the TIF_* bits in arch code, > and we don't do that for other bits that are only used in some configurations > (e.g. TIF_UPROBE). That's not just for aesthetics -- for example, on arm64 we > try to keep the TIF_WORK_MASK bits contiguous, which is difficult if a bit in > the middle doesn't exist in some configurations.
That's useful to know. And, I think you are right about the ugliness of this.
> Is it painful to organise the common code so that arch code can define > TIF_NEED_RESCHED_LAZY regardless of whether CONFIG_PREEMPT_AUTO is selected?
So, the original reason I did it this way was because I wanted to have zero performance impact on !CONFIG_PREEMPT_AUTO configurations whether TIF_NEED_RESCHED_LAZY was defined or not. (I was doing some computation with TIF_NEED_RESCHED_LAZY at that point.)
Eventually I changed that part of code but this stayed.
Anyway, this should be easy enough to fix with done #ifdefry.
Thanks for reviewing.
-- ankur
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