Messages in this thread | | | Date | Mon, 02 Jun 2008 16:04:21 -0700 | From | Max Krasnyansky <> | Subject | Re: Inquiry: Should we remove "isolcpus= kernel boot option? (may have realtime uses) |
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Peter Zijlstra wrote: > On Tue, 2008-06-03 at 00:35 +0200, Ingo Oeser wrote: >> Hi Paul, >> >> in short: NAK! >> >> On Monday 02 June 2008, Paul Jackson wrote: >>> (Aside to the RealTime folks -- is there a 'realtime' >>> email list which I should include in this discussion?) >>> >>> The kernel has a "isolcpus=" kernel boot time parameter. This >>> parameter isolates CPUs from scheduler load balancing, minimizing the >>> impact of scheduler latencies on realtime tasks running on those CPUs. >> I used it to mask out a defect CPU on a 8-CPU node of a >> HPC-cluster at a customer site, until the $BIG_VENDOR >> sent a replacement. And to prove $BIG_VENDOR, that we actually >> have a problem on THAT CPU. >> >> So I would really like to keep this fault isolation capability. >> I made my customer happy with that. >> >> I wish Linux had more such "mask out bad hardware" features >> to faciliate fault isolation and boot and runtime. > > Yeah - except that its not meant to be used as such - it will still > brings the cpu up, and it is still usable for the OS. > > So sorry, your abuse doesn't make for a case to keep this abomination.
Ingo, I just wanted to elaborate on what Peter is saying. That CPU will still have to be _booted_ properly. It may be used for hard- and soft- interrupt processing, workqueues (internal kernel queuing mechanism) and kernel timers.
In your particular case you're much much much better off with doing echo 0 > /sys/devices/system/cpuN/online either during initrd stage or as a first init script. That way bad cpu will be _completely_ disabled.
Max
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