Messages in this thread | | | From | Dieter Nützel <> | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable | Date | Tue, 15 Jan 2002 00:42:56 +0100 |
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George Anzinger wrote: > jogi@planetzork.ping.de wrote: > > That's the second test I am normally running. Just running xmms while > > doing the kernel compile. I just wanted to check if the system slows > > down because of preemption but instead it compiled the kernel even > > faster :-) > > This sort of thing is nice to hear, but, it does show up a problem in > the non-preempt kernel. That preemption improves compile performance > implies that the kernel is not doing the right thing during a normal > compile and that preemption, to some extent, corrects the problem. But > preemption adds the overhead of additional context switches. It would > be nice to know where the time is coming from. I.e. lets assume that > the actual compile takes about the same amount of execution time with or > without preemption.
That's the case in most of my "benchmarks".
e.g. dbench 32:
2.4.18-pre3 sched-O1-2.4.17-H7.patch 10_vm-22 00_nanosleep-5 bootmem-2.4.17-pre6 read-latency.patch waitq-2.4.17-mainline-1 plus all 2.4.18-pre3.pending ReiserFS stuff
Throughput 41.5565 MB/sec (NB=51.9456 MB/sec 415.565 MBit/sec) 14.860u 48.320s 1:41.66 62.1% 0+0k 0+0io 938pf+0w
with preempt+lock-break
Throughput 47.0049 MB/sec (NB=58.7561 MB/sec 470.049 MBit/sec) 14.280u 49.370s 1:30.88 70.0% 0+0k 0+0io 939pf+0w
user: nearly equally system: 1 second more with preempt+lock-break all: 11 less with preempt+lock-break
> Then for the preemptable kernel to do the job > faster something else must go up, idle time perhaps. If this is the > case, then there is some place in the kernel that is wasting cpu time > and that is preemptable and the preemptable patch is moving this idle > time to the idle process.
> What ever the reason, while I do want to promote preemption, I think we > should look at this issue and, at the very least, explain it.
What do you think about IO-wait for top/ps like SUN have? Do you think we lost CPU cycles, there?
-- Dieter Nützel Graduate Student, Computer Science
University of Hamburg Department of Computer Science @home: Dieter.Nuetzel@hamburg.de - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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