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Message-ID: <20140809140426.GA20995@kroah.com> Date: Sat, 9 Aug 2014 07:04:26 -0700 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: Peng Tao <bergwolf@...il.com> Cc: Oleg Drokin <green@...uxhacker.ru>, Evgeny Budilovsky <budevg@...il.com>, "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>, Andreas Dilger <andreas.dilger@...el.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Lai Siyao <lai.siyao@...el.com> Subject: Re: [PATCH] staging/lustre: use rcu_dereference to access rcu protected current->real_parent field On Sat, Aug 09, 2014 at 07:05:46PM +0800, Peng Tao wrote: > On Fri, Aug 8, 2014 at 1:32 PM, Greg Kroah-Hartman > <gregkh@...uxfoundation.org> 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? Because maybe these stats preceed the introduction of perf and other tracing/debug tools? I don't know, it's really low down on the list of reasons why lustre can't be merged out of staging at the moment, you all have much bigger issues to address first. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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