Re: [PATCH] staging/lustre: use rcu_dereference to access rcu protected current->real_parent field

[Peng Tao]

On Fri, Aug 8, 2014 at 1:32 PM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, Aug 08, 2014 at 01:06:15AM -0400, Oleg Drokin wrote:
>>
>> On Aug 8, 2014, at 12:42 AM, Greg Kroah-Hartman wrote:
>>
>> > On Fri, Aug 08, 2014 at 12:03:20AM -0400, Oleg Drokin wrote:
>> >> Hello!
>> >>
>> >> On Aug 7, 2014, at 11:49 PM, Greg Kroah-Hartman wrote:
>> >>>>
>> >>>> This is not a critical bug and in the worst case the code here may
>> >>>> cause miss of statistics counter increase.
>> >>>> This is why I think it is not worth to backport the patch at all.
>> >>> You are right, and if this is just for some random "statistics" file,
>> >>> can we just delete the whole function?
>> >>
>> >> I hope not!
>> >> This is used all around the client to tally up various operations executed counts.
>> > Why would you do that?  Why would they care?
>>
>> We would do that to provide information on the client operations performed.
>> They would care because they are interested in what particular clients might be doing.
>>
>> >> The statistic is then used by various userspace monitoring tools.
>> > Why not use the in-kernel monitoring tools instead of creating your own?
>> > What does userspace do with that information?
>>
>> We don't really control the userspace tools. People write tools to suit their needs
>> to monitor loads, see odd things the end users are doing or possibly for some
>> debugging even.
>> Correlating these numbers with what server sees also proves useful at times
>> (write combining for example).
>>
>> Here's a sample of output of a recently mounted client that I poked on a bit (the lines starting with # are my comments):
>> # cat /proc/fs/lustre/llite/lustre-ffff88008dde27f0/stats
>> snapshot_time             1407473168.466102 secs.usecs
>> read_bytes                1 samples [bytes] 0 0 0
>> write_bytes               4 samples [bytes] 2 7 19
>> osc_write                 4 samples [bytes] 2 7 19
>> # The bytes counts show you minimum, maximum of writes seen and total number of bytes read-written.
>> # Lustre (and many other network filesystems) is very sensitive to small IO, esp. reads so it's good
>> # to know if you have a lot of it.
>> open                      6 samples [regs]
>> # The "regs" type just shows you how many of given type operations were performed since last statistic reset.
>> # Frequently that allows people to guess where does high load come from on a particular client when
>> # it's otherwise not obvious because not a lot of cpu is used.
>> # Some operations are heavier than others too.
>> close                     6 samples [regs]
>> readdir                   4 samples [regs]
>> setattr                   1 samples [regs]
>> truncate                  4 samples [regs]
>> getattr                   7 samples [regs]
>> create                    1 samples [regs]
>> alloc_inode               1 samples [regs]
>> getxattr                  8 samples [regs]
>> inode_permission          28 samples [regs]
>>
>> As more operations types are seen the list grows.
>> Then there are also specific stats for readahead (data and metadata) so that interested people can make informed
>> decisions on the tuning there should they be unsatisfied with default settings.
>>
>> I am not sure there's a similar mechanism in the kernel already that
>> would allow us to get this sort of data easily all in one place?
>
> perf should show you this, if not, please add the functionality there.
> A filesystem is not the place to have performance monitoring code, this
> needs to be removed before it can be moved out of staging.  Please work
> with the trace/perf developers on this if there is something lacking
> there.
>
nfs and nfsd track rpc ops statistics and export them via
/proc/self/mountstats, e.g.,

device 192.168.214.141:/d9691564-432b-11e2-8e5d-8b7acf882df3 mounted
on /mnt/pnfsd with fstype nfs4 statvers=1.1
        opts: rw,vers=4.1,rsize=262144,wsize=262144,namlen=255,acregmin=3,acregmax=60,acdirmin=30,acdirmax=60,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.214.128,local_lock=none
        age:    15426
        impl_id:        name='',domain='',date='0,0'
        caps:   caps=0x3ffff,wtmult=512,dtsize=32768,bsize=0,namlen=255
        nfsv4:  bm0=0xfdffbfff,bm1=0x40f9be3e,bm2=0x803,acl=0x3,sessions
        sec:    flavor=1,pseudoflavor=1
        events: 82474 12159573 9527 109202 7574 10119 16289648 3634869
10938 108551 2084272 182492 13646 7700 52594 60832 8829 48985 0 6564
1459053 66 0 0 0 289315 376376
        bytes:  11526471786 9942294760 3280371712 3278274560
14578366831 11710126268 2782400 2084272
        RPC iostats version: 1.0  p/v: 100003/4 (nfs)
        xprt:   tcp 859 0 2 0 12 408031 407999 29 2169734 0 32 2496 310753
        per-op statistics
                NULL: 0 0 0 0 0 0 0 0
                READ: 289327 289326 0 35877640 14615129136 63609 1800007 1893161
               WRITE: 376352 376360 0 11759732976 51184768 6698277
2246445 8978314
              COMMIT: 3076 3076 0 381424 393728 1827 15450 17329
                OPEN: 24926 24926 0 7329252 8968144 1373312 1794621 3169378
<snip...>

Why Lustre cannot do similar things?

Thanks,
Tao

> thanks,
>
> greg k-h
> dG
>
>>
>> Bye,
>>     Oleg
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