Messages in this thread | | | Subject | Re: High CPU load when machine is idle (related to PROBLEM: Unusually high load average when idle in 2.6.35, 2.6.35.1 and later) | From | Chase Douglas <> | Date | Thu, 14 Oct 2010 11:29:21 -0400 |
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On Thu, 2010-10-14 at 16:58 +0200, Damien Wyart wrote: > Hello, > > > With 2.6.36-rc6, I'm seeing a load of around 0.60 when the machine is > > completely idle. This is similar to what someone reported for the latest > > 2.6.35.x stables. This is on a core i7 machine, but I've no time to > > bisect or test earlier versions right now, but I guess this is easy to > > reproduce on the same plateform. > > After further investigation and cross-checking with the thread "PROBLEM: > Unusually high load average when idle in 2.6.35, 2.6.35.1 and later", > I came to the following results: > > - the commit 74f5187ac873042f502227701ed1727e7c5fbfa9 isolated by Tim > seems to be the culprit; > - reverting it solves the problem with 2.6.36-rc7 in NOHZ mode: the load > when idle goes down to 0.00 (which it never does with the patch > applied) > - using nohz=no with the commit reverted still gives correct behaviour > (tested just in case) > > - vanilla 2.6.36-rc7 with this commit applied has the problem (load is > around 0.60 when machine idle, sometimes less after several hours > of uptime, but never 0.00), and rebooting with nohz=no makes the > problem disappear: load goes down to 0.00 quickly after boot process > has finished. > > I hope this answers the questions raised in the Tim's thread. > > Could someone with knowledge of the commit take a look at the problem? > It would be a bit annoying to have this problem in 2.6.36, since Tim's > initial report dates back to 2 weeks ago... > > I can help for further testing if needed.
Sorry I haven't been as responsive to this issue as I would have liked. I've been rather busy on other work.
My biggest testing concern is that in reality, load on a normal desktop machine (i.e. not some stripped down machine disconnected from network or any other input running nothing but busybox) should not be 0.00. Maybe load on a server doing absolutely nothing could be 0.00, but there's usually something going on that should bump it up to a few hundredths. Watch top, and if you see at least 1% constant cpu usage there, your load average should be at least 0.01. That said, there does seem to be a bug somewhere as a load of 0.60 on an idle machine seems high.
-- Chase
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