On Sat, Oct 31, 2015 at 03:15:23PM +0200, Noam Camus wrote:
> From: Tal Zilcer <[email protected]>
>
> Since the CTOP is SMT hardware multi-threaded, we need to hint
> the HW that now will be a very good time to do a hardware
> thread context switching. This is done by issuing the schd.rw
> instruction (binary coded here so as to not require specific
> revision of GCC to build the kernel).
> sched.rw means that Thread becomes eligible for execution by
> the threads scheduler after all pending read/write
> transactions were completed.
>
> Signed-off-by: Noam Camus <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> ---
> arch/arc/include/asm/processor.h | 5 +++++
> 1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h
> index 7266ede..f1a51a6 100644
> --- a/arch/arc/include/asm/processor.h
> +++ b/arch/arc/include/asm/processor.h
> @@ -58,7 +58,12 @@ struct task_struct;
> * get optimised away by gcc
> */
> #ifdef CONFIG_SMP
> +#ifdef CONFIG_EZNPS_MTM_EXT
> +#define cpu_relax() \
> + __asm__ __volatile__ (".word %0" : : "i"(CTOP_INST_SCHD_RW) : "memory")
> +#else
> #define cpu_relax() __asm__ __volatile__ ("" : : : "memory")
> +#endif
> #else
> #define cpu_relax() do { } while (0)
> #endif
At which point you might want to revisit:
arch/arc/include/asm/processor.h:#define cpu_relax_lowlatency() cpu_relax()
From: Peter Zijlstra [mailto:[email protected]]
Sent: Monday, November 02, 2015 11:22 AM
> At which point you might want to revisit:
> arch/arc/include/asm/processor.h:#define cpu_relax_lowlatency() cpu_relax()
Thanks, I will define this as barrier since cpu_relax() may take out current logical CPU for many cycles.