Messages in this thread | | | Date | Tue, 22 May 2012 11:06:06 -0400 | From | Vivek Goyal <> | Subject | Re: [RFC] block/throttle: Add IO throttled information in blkcg. |
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On Tue, May 22, 2012 at 10:44:11PM +0800, Tao Ma wrote: > Hi Vivek, > Thanks for the quick response. > On 05/22/2012 07:11 PM, Vivek Goyal wrote: > > On Tue, May 22, 2012 at 04:10:36PM +0800, Tao Ma wrote: > >> From: Tao Ma <boyu.mt@taobao.com> > >> > >> Currently, if the IO is throttled by io-throttle, the SA has no idea of > >> the situation and can't report it to the real application user about > >> that he/she has to do something. So this patch adds a new interface > >> named blkio.throttle.io_throttled which indicates how many IOs are > >> currently throttled. > > > > If the only purpose is to know whether IOs are being throttled, why > > not just scan for the rules and see if respective device has any > > throttling rules or not. > Sorry, but setting a throttling rules doesn't mean the IOs are > throttled, right? So scanning doesn't work here IMHO.
It means IOs will be throttled if you cross a certain rate. But yes, it does not give any information that if at time T if there are any bios throttled in the queue or not.
> > > > Even if you introduce this interface, you will end up scanning for > > throttled ios against that particular device. And if IO is not happening > > at that moment or if IO rate is not exceeding the rate limit, there > > might not be any throttled ios and one might get misled. > Oh, no actually in a *clound computing* environment, it is really > useful, not misled. So let me describe it in more detail. Our product > system will limit every instance to an approximate number at first, and > then watch out the IOs being throttled. If these numbers is high, it can: > 1) Shout loudly to the application programmer about the abuse if he > sends out too much IO requests. > 2) If it is not too much and some other instances are not active, adjust > the throttled ratio so that this instance can work much faster.
Ok, so you want to use this more as "congestion" parameter which tells at a given moment how busy the queue is, or in this instance how many IOs are backlogged in a cgroup due to throttling limits.
I guess, it is not a bad idea to export this stat then. Will "blkio.throttle.queued" be a better name to reflect that how many bios are currently queued in throttling layer of request queue.
Thanks Vivek
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