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Date: Tue, 9 Jul 2002 16:23:51 -0700 (PDT)
From: Julian Elischer <julian@elischer.org>
To: Bruce Evans <bde@zeta.org.au>
Cc: John Baldwin <jhb@FreeBSD.ORG>,
	FreeBSD current users <current@FreeBSD.ORG>,
	FreeBSD current users <current@FreeBSD.ORG>
Subject: RE: userret() , ast() and the end of syscalls
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On Wed, 10 Jul 2002, Bruce Evans wrote:

> On Tue, 9 Jul 2002, Julian Elischer wrote:
> 
> > On Wed, 10 Jul 2002, Bruce Evans wrote:
> >
> > > Hopefully there won't be any unconditional code.  Unconditional code
> > > in userret() pessimizes all syscalls.  Unconditional code added by KSEIII
> > > pessimized basic syscall overhead by 10% according to lmbench2.
> >
> > Mostly it's conditional..
> > 	if (p->p_flag & P_KSES)
> > in syscall()
> > and
> > 	if (p->p_flag & P_KSES) {
> > in userret()
> 
> The conditionals are unconditional, and together with the proc locking)
> (mainly the locking) are what gives the 10% pessimization.  It would be
> much more than 10% to actually do something :).
> 
> > it's probably
> >         PROC_LOCK(p);
> >         thread_suspend_check(0);        /* Can suspend or kill */
> >         PROC_UNLOCK(p);
> >
> >
> > try replace it with:
> >         if (P_SHOULDSTOP(p) {
> >                 PROC_LOCK(p);
> >                 thread_suspend_check(0);        /* Can suspend or kill */
> >                 PROC_UNLOCK(p);
> >         }
> 
> Can these flags be changed asynchronously?  If so, then everything needs
> to be handled by ast() anyway.  userret() should only check for work that
> needs doing in the usual case, and hopefully there is none (except for
> things like ktrace).

That (use ast) is a sensible suggestion. I guess it belongs 
with the postsig in ast().
I can try that..  though it ;ll take a little work
in the mean time try the patch above with lmbench..


> 
> Bruce
> 
> 


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