Problem with HT support in 5.4

[Kris Kennaway]

On Fri, May 27, 2005 at 09:30:46AM -0500, Jacob S wrote:
> On Fri, 27 May 2005 18:05:48 +0400
> Dmitry Mityugov <dmitry.mityugov at gmail.com> wrote:
> 
> > On 5/27/05, Jacob S wrote:
> > > Hello list,
> > > 
> > > I upgraded a few 5.3 servers to 5.4 yesterday and everything seemed
> > > to go well. After booting the new kernel, dmesg correctly showed 2
> > > logical cpus (1 xeon with HT).
> > > 
> > > However, when I look at top's output, it always shows at least 50%
> > > cpu idle time - even when the load is above 10. To confirm this, I
> > > ran burnP6 from the cpuburn port - even with over a hundred apache
> > > processes going, exim running and a few other things, top still
> > > reported the cpu as 50% idle. The 'C' column in top, between 'State'
> > > and 'Time' also shows everything as being run on cpu 0.
> > > 
> > > `ps ax | grep cpu` reports this:
> > >  11  ??  RL     0:00.00 [idle: cpu1]
> > >  12  ??  RL   931:45.24 [idle: cpu0]
> > > 108  ??  DL     0:04.02 [schedcpu]
> > > 
> > > So it looks like smp support is enabled and it sees the HT enabled
> > > processor, but it's not using the second logical cpu. Is there
> > > something I missed in compiling the kernel, or is this a bug? I have
> > > confirmed it on two 5.4 servers now.
> > 
> > Oh, wait, it is probably just the last HT security patch,
> > ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:09.htt.asc.
> 
> hmm... So basically, SMP can be enabled, but it won't use HT even if it
> sees a capable processor? 

By default..it's a trivial matter of setting a loader tunable.  Please
read the advisory.

Kris
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