svn commit: r300110 - head/sys/kern

[NGie Cooper]

> On May 17, 2016, at 20:55, Mark Johnston <markj at FreeBSD.org> wrote:
> 
> Author: markj
> Date: Wed May 18 03:55:54 2016
> New Revision: 300110
> URL: https://svnweb.freebsd.org/changeset/base/300110
> 
> Log:
>  Do not acquire the thread lock in hardclock_cnt() unless needed.
> 
>  This function only sets thread flags if a SIGPROF or SIGVTALRM timer
>  has fired, which is almost never the case.
> 
>  MFC after:    2 weeks
> 
> Modified:
>  head/sys/kern/kern_clock.c
> 
> Modified: head/sys/kern/kern_clock.c
> ==============================================================================
> --- head/sys/kern/kern_clock.c    Wed May 18 03:50:21 2016    (r300109)
> +++ head/sys/kern/kern_clock.c    Wed May 18 03:55:54 2016    (r300110)
> @@ -570,9 +570,11 @@ hardclock_cnt(int cnt, int usermode)
>            flags |= TDF_PROFPEND | TDF_ASTPENDING;
>        PROC_ITIMUNLOCK(p);
>    }
> -    thread_lock(td);
> -    td->td_flags |= flags;
> -    thread_unlock(td);
> +    if (flags != 0) {
> +        thread_lock(td);
> +        td->td_flags |= flags;
> +        thread_unlock(td);
> +    }

Use predict_false?
> 
> #ifdef    HWPMC_HOOKS
>    if (PMC_CPU_HAS_SAMPLES(PCPU_GET(cpuid)))
>