Messages in this thread | | | Date | Tue, 10 Sep 2013 11:03:49 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 9/9] x86/UV: Add ability to disable UV NMI handler |
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On Mon, Sep 09, 2013 at 10:07:03AM -0700, Mike Travis wrote: > > > On 9/9/2013 5:43 AM, Peter Zijlstra wrote: > > On Thu, Sep 05, 2013 at 05:50:41PM -0500, Mike Travis wrote: > >> For performance reasons, the NMI handler may be disabled to lessen the > >> performance impact caused by the multiple perf tools running concurently. > >> If the system nmi command is issued when the UV NMI handler is disabled, > >> the "Dazed and Confused" messages occur for all cpus. The NMI handler is > >> disabled by setting the nmi disabled variable to '1'. Setting it back to > >> '0' will re-enable the NMI handler. > > > > I'm not entirely sure why this is still needed now that you've moved all > > really expensive bits into the UNKNOWN handler. > > > > Yes, it could be considered optional. My primary use was to isolate > new bugs I found to see if my NMI changes were causing them. But it > appears that they are not since the problems occur with or without > using the NMI entry into KDB. So it can be safely removed.
OK, as a debug option it might make sense, but removing it is (of course) fine with me ;-)
> (The basic problem is that if you hang out in KDB too long the machine > locks up.
Yeah, known issue. Not much you can do about it either I suspect. The system generally isn't build for things like that.
> Other problems like the rcu stall detector does not have a > means to be "touched" like the nmi_watchdog_timer so it fires off a > few to many, many messages.
That however might be easily cured if you ask Paul nicely ;-)
> Another, any network connections will time > out if you are in KDB more than say 20 or 30 seconds.) > > One other problem is with the perf tool. It seems running more than > about 2 or 3 perf top instances on a medium (1k cpu threads) sized > system, they start behaving badly with a bunch of NMI stackdumps > appearing on the console. Eventually the system become unusable.
Yuck.. I haven't seen anything like that on the 'tiny' systems I have :/
> On a large system (4k), the perf tools get an error message (sorry > don't have it handy at the moment) the basically implies that the > perf config option is not set. Again, I wanted to remove the new > NMI handler to insure that it wasn't doing something weird, and > it wasn't.
Cute..
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