On 07/18/2012 01:25 AM, Jonathan Nieder wrote: > Anders Boström wrote: > >> Starting with 3.2.17-1, the CPU load accounting is broken when the >> computer is idle. The CPU load is reported as >0.50 when >> idle. 3.2.16-1 don't suffer from this problem. >> >> Suspected patch is the upstream patch >> "sched: Fix nohz load accounting -- again!" >> commit 5e2d50da11f0e6ec3ce8fe658d7c83b0b4346c68 to 3.2 and >> originating from c308b56b5398779cd3da0f62ab26b0453494c3d4 . > > Please test the attached patch against a 3.2.y kernel, for example > following the instructions below: Good news everyone. I have tested kernel 3.2.21 and the attached patch (based on 5167e8d I presume) seems to be fixing all the load average oddities. I've compiled following kernels: * 3.2.21-hz (CONFIG_NO_HZ=n) * 3.2.21-no-hz (CONFIG_NO_HZ=y) * 3.2.21-no-hz-5167e8d (CONFIG_NO_HZ=y) + attached patch The load reported by 3.2.21-hz and 3.2.21-no-hz-5167e8d is exactly the same under different CPU usage. Without the patch the tickless kernel tends to show lower load values than what you would expect. I can't say much for the case when load is too high on an idle machine, because I haven't been able to reproduce the problem in the first place. To summarize: the bug is present in unpatched kernel and fixed by applying the attached patch. No nasty side effects noticed. -- Lesław Kopeć
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