svn commit: r189374 - user/kmacy/HEAD_fast_net_merge/sys/netinet

[John Baldwin]

On Wednesday 04 March 2009 6:20:55 pm Kip Macy wrote:
> Do we have any mechanism for handling sparse cpuids?
> If so I can do modulo the number of active cpus and then taking that
> value as an index. If not its a bit of an academic observation.
> 
> -Kip

The rest of the kernel is careful to handle sparse cpuids already.  You can 
use CPU_ABSENT() to see if a CPU is present or not.  You cound pre-populate a 
table during boot if you wished by doing something like:

int	active_cpus[MAXCPU];

sysinit_foo()
{
	int i, cpu;

	i = 0;
	for (cpu = 0; cpu <= mp_maxid; cpu++) {
		if (CPU_ABSENT(cpu)
			continue;
		active_cpus[i] = cpu;
		i++;
	}
	KASSERT(i == mp_ncpu, ("bad juju"));
}

Then you could use (active_cpus[flowid & mp_ncpu]) as a CPU.  Eventually when 
we support removing and adding CPUs at runtime (or disabling/enabling them at 
runtime) there will be eventhandlers that you can hook to adjust your 
active_cpus array.
 
> On Wed, Mar 4, 2009 at 2:59 PM, John Baldwin <jhb at freebsd.org> wrote:
> > On Wednesday 04 March 2009 4:22:39 pm Kip Macy wrote:
> >> Author: kmacy
> >> Date: Wed Mar  4 21:22:39 2009
> >> New Revision: 189374
> >> URL: http://svn.freebsd.org/changeset/base/189374
> >>
> >> Log:
> >>   Use per-cpu callouts for tcp_timer
> >>   186694, 187660
> >>
> >>   186694:
> >>   - convert tcp_timer_activate over to using
> >>     per-cpu callouts
> >>   - don't acquire the tcbinfo lock exclusively
> >>     in tcp_timer_rexmt unless needed for tcp_drop
> >>
> >>   187660:
> >>   - mp_maxid may not be valid ensure that we
> >>     re-schedule on cpuid less than or equal to
> >>     the current one for tcp callouts
> >>
> >> Modified:
> >>   user/kmacy/HEAD_fast_net_merge/sys/netinet/tcp_timer.c
> >>
> >> Modified: user/kmacy/HEAD_fast_net_merge/sys/netinet/tcp_timer.c
> >>
> > 
==============================================================================
> >> --- user/kmacy/HEAD_fast_net_merge/sys/netinet/tcp_timer.c    Wed Mar  4
> > 21:04:52 2009   (r189373)
> >> +++ user/kmacy/HEAD_fast_net_merge/sys/netinet/tcp_timer.c    Wed Mar  4
> > 21:22:39 2009   (r189374)
> >> @@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$");
> >>  #include <sys/mbuf.h>
> >>  #include <sys/mutex.h>
> >>  #include <sys/protosw.h>
> >> +#include <sys/smp.h>
> >>  #include <sys/socket.h>
> >>  #include <sys/socketvar.h>
> >>  #include <sys/sysctl.h>
> >> @@ -118,6 +119,8 @@ int       tcp_maxpersistidle;
> >>       /* max idle time in persist */
> >>  int  tcp_maxidle;
> >>
> >> +#define      INP_CPU(inp)    min(curcpu, ((inp)->inp_flowid % mp_maxid))
> >
> > This is not really safe.  CPU ID's may be sparse.  The only guarantees you
> > have are that 0 is the boot CPU, and that all valid CPU IDs are in the 
range
> > [0 .. mp_maxid] (inclusive).  Thus, you could have a system that only has
> > CPUs 0 and 3 and if you are on CPU 3 and flowid is 5, then this will 
choose
> > min(3, 5 % 3) == min(3, 2) == 2 which is an invalid CPU.
> >
> > --
> > John Baldwin
> >
> 



-- 
John Baldwin