Messages in this thread | | | Date | Thu, 10 May 2012 10:40:05 +0200 | From | Pascal Chapperon <> | Subject | Re: RCU related performance regression in 3.3 |
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Le 05/05/2012 01:14, Paul E. McKenney a écrit : > On Fri, May 04, 2012 at 11:41:13PM +0200, Pascal Chapperon wrote: >> Le 04/05/2012 17:04, Paul E. McKenney a écrit : >>> On Fri, May 04, 2012 at 04:42:54PM +0200, Pascal Chapperon wrote: >>>> Le 01/05/2012 17:45, Paul E. McKenney a écrit : >>>> >>>>> Here is my RCU_FAST_NO_HZ patch stack on top of v3.4-rc4. >>>>> >>>>> Or you can pull branch fnh.2012.05.01a from: >>>>> >>>>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git >>>>> >>>>> Thanx, Paul >>>>> >>>> I applied your global patch on top of v3.4-rc4. But the slowdown is >>>> worse than before : boot sequence took 80s instead 20-30s (12s for >>>> initramfs instead of 2s). >>>> >>>> I'll send you rcu tracing log in a second mail. >>> >>> Hmmm... Well, I guess I am glad that I finally did something that >>> had an effect, but I sure wish that the effect had been in the other >>> direction! >>> >>> Just to make sure I understand: the difference between the 20-30s and >>> the 80s is exactly the patch I sent you? >>> >>> Thanx, Paul >>> >>> >> Yes. Exactly same kernel config as in previous results, I applied >> your patch against v3.4-rc4, and sorry, the result is exactly what I >> said; >> I saw that your global patch was quite huge, and addresses things which >> are not directly related with the initial patch (commit >> 7cb92499000e3c86dae653077b1465458a039ef6); maybe a side effect? >> >> However, I'm ready to try this patch on my smaller laptop which >> supports well CONFIG_FAST_NO_HZ=y and systemd, if you think it can >> help ? >> >> Another thought: this issue as nothing to do with i7 Hyper-threading >> capacities ? (as I test core2duo, Pentium ulv in same conditions and I >> don't encountered any slowdown ?) > > Well, one possibility is that your setup starts the jiffies counter > at some interesting value. The attached patch (also against v3.4-rc4) > applies a bit more paranoia to the initialization to handle this > and other possibilities. > > Thanx, Paul > > ------------------------------------------------------------------------ I tried your new patch against v3.4-rc5 and saw no improvement : still 75 s. for the boot sequence.
I'll send you the logs in a second mail.
Pascal
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