[PATCH RFC 00/11] makedumpfile: parallel processing
Chao Fan
cfan at redhat.com
Wed Dec 23 19:31:37 PST 2015
----- Original Message -----
> From: "HATAYAMA Daisuke" <d.hatayama at jp.fujitsu.com>
> To: cfan at redhat.com
> Cc: ats-kumagai at wm.jp.nec.com, zhouwj-fnst at cn.fujitsu.com, kexec at lists.infradead.org
> Sent: Thursday, December 24, 2015 11:22:28 AM
> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
>
> From: Chao Fan <cfan at redhat.com>
> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
> Date: Wed, 23 Dec 2015 21:20:48 -0500
>
> >
> >
> > ----- Original Message -----
> >> From: "HATAYAMA Daisuke" <d.hatayama at jp.fujitsu.com>
> >> To: cfan at redhat.com
> >> Cc: ats-kumagai at wm.jp.nec.com, zhouwj-fnst at cn.fujitsu.com,
> >> kexec at lists.infradead.org
> >> Sent: Tuesday, December 22, 2015 4:32:25 PM
> >> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
> >>
> >> Chao,
> >>
> >> From: Chao Fan <cfan at redhat.com>
> >> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
> >> Date: Thu, 10 Dec 2015 05:54:28 -0500
> >>
> >> >
> >> >
> >> > ----- Original Message -----
> >> >> From: "Wenjian Zhou/周文剑" <zhouwj-fnst at cn.fujitsu.com>
> >> >> To: "Chao Fan" <cfan at redhat.com>
> >> >> Cc: "Atsushi Kumagai" <ats-kumagai at wm.jp.nec.com>,
> >> >> kexec at lists.infradead.org
> >> >> Sent: Thursday, December 10, 2015 6:32:32 PM
> >> >> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
> >> >>
> >> >> On 12/10/2015 05:58 PM, Chao Fan wrote:
> >> >> >
> >> >> >
> >> >> > ----- Original Message -----
> >> >> >> From: "Wenjian Zhou/周文剑" <zhouwj-fnst at cn.fujitsu.com>
> >> >> >> To: "Atsushi Kumagai" <ats-kumagai at wm.jp.nec.com>
> >> >> >> Cc: kexec at lists.infradead.org
> >> >> >> Sent: Thursday, December 10, 2015 5:36:47 PM
> >> >> >> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
> >> >> >>
> >> >> >> On 12/10/2015 04:14 PM, Atsushi Kumagai wrote:
> >> >> >>>> Hello Kumagai,
> >> >> >>>>
> >> >> >>>> On 12/04/2015 10:30 AM, Atsushi Kumagai wrote:
> >> >> >>>>> Hello, Zhou
> >> >> >>>>>
> >> >> >>>>>> On 12/02/2015 03:24 PM, Dave Young wrote:
> >> >> >>>>>>> Hi,
> >> >> >>>>>>>
> >> >> >>>>>>> On 12/02/15 at 01:29pm, "Zhou, Wenjian/周文剑" wrote:
> >> >> >>>>>>>> I think there is no problem if other test results are as
> >> >> >>>>>>>> expected.
> >> >> >>>>>>>>
> >> >> >>>>>>>> --num-threads mainly reduces the time of compressing.
> >> >> >>>>>>>> So for lzo, it can't do much help at most of time.
> >> >> >>>>>>>
> >> >> >>>>>>> Seems the help of --num-threads does not say it exactly:
> >> >> >>>>>>>
> >> >> >>>>>>> [--num-threads THREADNUM]:
> >> >> >>>>>>> Using multiple threads to read and compress data of
> >> >> >>>>>>> each
> >> >> >>>>>>> page
> >> >> >>>>>>> in parallel.
> >> >> >>>>>>> And it will reduces time for saving DUMPFILE.
> >> >> >>>>>>> This feature only supports creating DUMPFILE in
> >> >> >>>>>>> kdump-comressed format from
> >> >> >>>>>>> VMCORE in kdump-compressed format or elf format.
> >> >> >>>>>>>
> >> >> >>>>>>> Lzo is also a compress method, it should be mentioned that
> >> >> >>>>>>> --num-threads only
> >> >> >>>>>>> supports zlib compressed vmcore.
> >> >> >>>>>>>
> >> >> >>>>>>
> >> >> >>>>>> Sorry, it seems that something I said is not so clear.
> >> >> >>>>>> lzo is also supported. Since lzo compresses data at a high
> >> >> >>>>>> speed,
> >> >> >>>>>> the
> >> >> >>>>>> improving of the performance is not so obvious at most of time.
> >> >> >>>>>>
> >> >> >>>>>>> Also worth to mention about the recommended -d value for this
> >> >> >>>>>>> feature.
> >> >> >>>>>>>
> >> >> >>>>>>
> >> >> >>>>>> Yes, I think it's worth. I forgot it.
> >> >> >>>>>
> >> >> >>>>> I saw your patch, but I think I should confirm what is the
> >> >> >>>>> problem
> >> >> >>>>> first.
> >> >> >>>>>
> >> >> >>>>>> However, when "-d 31" is specified, it will be worse.
> >> >> >>>>>> Less than 50 buffers are used to cache the compressed page.
> >> >> >>>>>> And even the page has been filtered, it will also take a buffer.
> >> >> >>>>>> So if "-d 31" is specified, the filtered page will use a lot
> >> >> >>>>>> of buffers. Then the page which needs to be compressed can't
> >> >> >>>>>> be compressed parallel.
> >> >> >>>>>
> >> >> >>>>> Could you explain why compression will not be parallel in more
> >> >> >>>>> detail ?
> >> >> >>>>> Actually the buffers are used also for filtered pages, it sounds
> >> >> >>>>> inefficient.
> >> >> >>>>> However, I don't understand why it prevents parallel compression.
> >> >> >>>>>
> >> >> >>>>
> >> >> >>>> Think about this, in a huge memory, most of the page will be
> >> >> >>>> filtered,
> >> >> >>>> and
> >> >> >>>> we have 5 buffers.
> >> >> >>>>
> >> >> >>>> page1 page2 page3 page4 page5 page6
> >> >> >>>> page7
> >> >> >>>> .....
> >> >> >>>> [buffer1] [2] [3] [4] [5]
> >> >> >>>> unfiltered filtered filtered filtered filtered unfiltered
> >> >> >>>> filtered
> >> >> >>>>
> >> >> >>>> Since filtered page will take a buffer, when compressing page1,
> >> >> >>>> page6 can't be compressed at the same time.
> >> >> >>>> That why it will prevent parallel compression.
> >> >> >>>
> >> >> >>> Thanks for your explanation, I understand.
> >> >> >>> This is just an issue of the current implementation, there is no
> >> >> >>> reason to stand this restriction.
> >> >> >>>
> >> >> >>>>> Further, according to Chao's benchmark, there is a big
> >> >> >>>>> performance
> >> >> >>>>> degradation even if the number of thread is 1. (58s vs 240s)
> >> >> >>>>> The current implementation seems to have some problems, we should
> >> >> >>>>> solve them.
> >> >> >>>>>
> >> >> >>>>
> >> >> >>>> If "-d 31" is specified, on the one hand we can't save time by
> >> >> >>>> compressing
> >> >> >>>> parallel, on the other hand we will introduce some extra work by
> >> >> >>>> adding
> >> >> >>>> "--num-threads". So it is obvious that it will have a performance
> >> >> >>>> degradation.
> >> >> >>>
> >> >> >>> Sure, there must be some overhead due to "some extra work"(e.g.
> >> >> >>> exclusive
> >> >> >>> lock),
> >> >> >>> but "--num-threads=1 is 4 times slower than --num-threads=0" still
> >> >> >>> sounds
> >> >> >>> too slow, the degradation is too big to be called "some extra
> >> >> >>> work".
> >> >> >>>
> >> >> >>> Both --num-threads=0 and --num-threads=1 are serial processing,
> >> >> >>> the above "buffer fairness issue" will not be related to this
> >> >> >>> degradation.
> >> >> >>> What do you think what make this degradation ?
> >> >> >>>
> >> >> >>
> >> >> >> I can't get such result at this moment, so I can't do some further
> >> >> >> investigation
> >> >> >> right now. I guess it may be caused by the underlying implementation
> >> >> >> of
> >> >> >> pthread.
> >> >> >> I reviewed the test result of the patch v2 and found in different
> >> >> >> machines,
> >> >> >> the results are quite different.
> >> >> >
> >> >> > Hi Zhou Wenjian,
> >> >> >
> >> >> > I have done more tests in another machine with 128G memory, and get
> >> >> > the
> >> >> > result:
> >> >> >
> >> >> > the size of vmcore is 300M in "-d 31"
> >> >> > makedumpfile -l --message-level 1 -d 31:
> >> >> > time: 8.6s page-faults: 2272
> >> >> >
> >> >> > makedumpfile -l --num-threads 1 --message-level 1 -d 31:
> >> >> > time: 28.1s page-faults: 2359
> >> >> >
> >> >> >
> >> >> > and the size of vmcore is 2.6G in "-d 0".
> >> >> > In this machine, I get the same result as yours:
> >> >> >
> >> >> >
> >> >> > makedumpfile -c --message-level 1 -d 0:
> >> >> > time: 597s page-faults: 2287
> >> >> >
> >> >> > makedumpfile -c --num-threads 1 --message-level 1 -d 0:
> >> >> > time: 602s page-faults: 2361
> >> >> >
> >> >> > makedumpfile -c --num-threads 2 --message-level 1 -d 0:
> >> >> > time: 337s page-faults: 2397
> >> >> >
> >> >> > makedumpfile -c --num-threads 4 --message-level 1 -d 0:
> >> >> > time: 175s page-faults: 2461
> >> >> >
> >> >> > makedumpfile -c --num-threads 8 --message-level 1 -d 0:
> >> >> > time: 103s page-faults: 2611
> >> >> >
> >> >> >
> >> >> > But the machine of my first test is not under my control, should I
> >> >> > wait
> >> >> > for
> >> >> > the first machine to do more tests?
> >> >> > If there are still some problems in my tests, please tell me.
> >> >> >
> >> >>
> >> >> Thanks a lot for your test, it seems that there is nothing wrong.
> >> >> And I haven't got any idea about more tests...
> >> >>
> >> >> Could you provide the information of your cpu ?
> >> >> I will do some further investigation later.
> >> >>
> >> >
> >> > OK, of course, here is the information of cpu:
> >> >
> >> > # lscpu
> >> > Architecture: x86_64
> >> > CPU op-mode(s): 32-bit, 64-bit
> >> > Byte Order: Little Endian
> >> > CPU(s): 48
> >> > On-line CPU(s) list: 0-47
> >> > Thread(s) per core: 1
> >> > Core(s) per socket: 6
> >> > Socket(s): 8
> >> > NUMA node(s): 8
> >> > Vendor ID: AuthenticAMD
> >> > CPU family: 16
> >> > Model: 8
> >> > Model name: Six-Core AMD Opteron(tm) Processor 8439 SE
> >> > Stepping: 0
> >> > CPU MHz: 2793.040
> >> > BogoMIPS: 5586.22
> >> > Virtualization: AMD-V
> >> > L1d cache: 64K
> >> > L1i cache: 64K
> >> > L2 cache: 512K
> >> > L3 cache: 5118K
> >> > NUMA node0 CPU(s): 0,8,16,24,32,40
> >> > NUMA node1 CPU(s): 1,9,17,25,33,41
> >> > NUMA node2 CPU(s): 2,10,18,26,34,42
> >> > NUMA node3 CPU(s): 3,11,19,27,35,43
> >> > NUMA node4 CPU(s): 4,12,20,28,36,44
> >> > NUMA node5 CPU(s): 5,13,21,29,37,45
> >> > NUMA node6 CPU(s): 6,14,22,30,38,46
> >> > NUMA node7 CPU(s): 7,15,23,31,39,47
> >>
> >> This CPU assignment on NUMA nodes looks interesting. Is it possible
> >> that this affects performance of makedumpfile? This is just a guess.
> >>
> >> Could you check whether the performance gets imporoved if you run each
> >> thread on the same NUMA node? For example:
> >>
> >> # taskset -c 0,8,16,24 makedumpfile --num-threads 4 -c -d 0 vmcore
> >> vmcore-cd0
> >>
> > Hi HATAYAMA,
> >
> > I think your guess is right, but maybe your command has a little problem.
> >
> > From my test, the NUMA did affect the performance, but not too much.
> > The average time of cpus in the same NUMA node:
> > # taskset -c 0,8,16,24,32 makedumpfile --num-threads 4 -c -d 0 vmcore
> > vmcore-cd0
> > is 314s
> > The average time of cpus in different NUMA node:
> > # taskset -c 2,3,5,6,7 makedumpfile --num-threads 4 -c -d 0 vmcore
> > vmcore-cd0
> > is 354s
> >
>
> Hmm, according to some previous discussion, what we should see here is
> whether it affects performance of makedumpfile with --num-threads 1
> and -d 31. So you should need to compare:
>
> # taskset 0,8 makedumpfile --num-threads 1 -c -d 31 vmcore vmcore-d31
>
> with:
>
> # taskset 0 makedumpfile -c -d 0 vmcore vmcore-d31
>
> Also, I'm assuming that you've done these benchmark on kdump 1st
> kernel, not kdump 2nd kernel. Is this correct?
>
Hi HATAYAMA,
I test in the first kernel, not in the kdump second kernel.
Thanks,
Chao Fan
> > But I think if you want to use "--num-threads 4", the --cpu-list numbers
> > following "taskset -c" should be 5 cpus at least, otherwise the time will
> > be too
> > long.
> >
>
> I see.
>
> --
> Thanks.
> HATAYAMA, Daisuke
>
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