Messages in this thread | | | Date | Fri, 3 Feb 2012 17:23:29 -0500 | From | Vivek Goyal <> | Subject | Re: [PATCH UPDATED 11/11] blkcg: unify blkg's for blkcg policies |
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On Fri, Feb 03, 2012 at 02:14:09PM -0800, Tejun Heo wrote: > On Fri, Feb 03, 2012 at 04:53:49PM -0500, Vivek Goyal wrote: > > Hmm... then blkiocg_reset_stats() will run into lock ordering issue. Can't > > hold queue lock inside blkcg lock. I guess you will do some kind of > > locking trick again as you did for io context logic. > > Ummm... I don't know the details yet but decisions like making > policies per-queue are much higher level than locking details. There > are cases where implementation details become problematic enough and > high level decisions are affected but I don't really think that would > be the case here. It's not like reset stats is a hot path. In fact, > I don't even understand why the hell we have it. I guess it's another > blkcg braindamage.
git commit of when it was added.
commit 84c124da9ff50bd71fab9c939ee5b7cd8bef2bd9 Author: Divyesh Shah <dpshah@google.com> Date: Fri Apr 9 08:31:19 2010 +0200
.. o add a separate reset_stats interface ..
> > If userland is interested in delta between certain periods, it's > supposed to read values at the start and end of the period and > subtract. Allowing reset might make sense if there's single bearded > admin looking at the raw numbers, but it breaks as soon as tools and > automation are involved. How would you decide who owns those > counters? >
Personally I consider it to be a debugging aid. User space applications should do what you suggested and that is take delta between certain periods.
Frankly speaking I have found it useful though. If I am debugging something, I don't have to reboot the system to reset the stats and calculating the difference from zero is easier for humans.
Thanks Vivek
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