Re: svn commit: r300110 - head/sys/kern

2016-05-18 Thread Mark Johnston 
On Tue, May 17, 2016 at 10:22:18PM -0700, NGie Cooper wrote:
> 
> > On May 17, 2016, at 20:55, Mark Johnston  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.cWed May 18 03:50:21 2016(r300109)
> > +++ head/sys/kern/kern_clock.cWed 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?

I don't think that's really warranted here. A __predict_false could
become incorrect after a future change elsewhere in this function, and
this isn't enough of a hot path for such a change to make a measurable
difference on its own.

> > 
> > #ifdefHWPMC_HOOKS
> >if (PMC_CPU_HAS_SAMPLES(PCPU_GET(cpuid)))
> > 
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Re: svn commit: r300110 - head/sys/kern

2016-05-17 Thread NGie Cooper 

> On May 17, 2016, at 20:55, Mark Johnston  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.cWed May 18 03:50:21 2016(r300109)
> +++ head/sys/kern/kern_clock.cWed 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?
> 
> #ifdefHWPMC_HOOKS
>if (PMC_CPU_HAS_SAMPLES(PCPU_GET(cpuid)))
> 
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svn commit: r300110 - head/sys/kern

2016-05-17 Thread Mark Johnston 
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);
+   }
 
 #ifdef HWPMC_HOOKS
if (PMC_CPU_HAS_SAMPLES(PCPU_GET(cpuid)))
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